Mitsuru and Kokoro have known each other since their childhood days in the Garden, but they barely knew each other and didn’t interact much. At the age of 14, they were assigned to the same FRANXX squad. Still, they barely interacted with each other as they had little need to and shared no common interests. Mitsuru was a lone wolf who had little to no need for his comrades and was unafraid to speak his opinion. On the other hand, Kokoro was a shy, quiet girl who was afraid to say her true feelings, usually going with the flow to get along with her comrades.
After Mitsuru got injured and traumatized from piloting with Zero Two, Kokoro started showing concern for Mitsuru's well being. He walked away during a briefing in the living room as everyone praised Hiro for successfully piloting with Zero Two, but everyone besides Kokoro failed to notice. She later found him sulking in the greenhouse and offered to listen to his problems. Kokoro commented she found Mitsuru's independence admirable, although Mitsuru misinterpreted it as pity and told her to leave him alone as he walked away.
When Squad 13 was rewarded with a short getaway at the beach, Mitsuru found the remains of an abandoned city and told his squadmates, in hopes of exploring the place. Kokoro voiced her fears of the cavern, to which Mitsuru replied she didn't need to come if she was afraid, explaining he couldn't guarantee anyone's safety. However, Mitsuru managed to save Kokoro from getting crushed by a falling bookcase in an old clinic later on, implying he had been following her closely. He also noticed Kokoro had picked up a book about childbirth and reproduction - banned information but chose not to mention it.
After a battle in which the girls’ parasite suits melted in front of the boys, Kokoro was embarrassed when Futoshi remarked he wasn’t ogling her because he found her to be beautiful. Upon hearing this, Mitsuru called him an idiot before walking away.
During the Boys x Girls fight, Kokoro and Mitsuru bumped into each other at the greenhouse. Mitsuru explained he was at the greenhouse as it was a good hiding place. Upon hearing this, Kokoro tried to initiate a conversation with him and chatted about the language of flowers. When she realized Mitsuru didn't seem to be listening, she asked if she was bothering him because of the fight. Mitsuru replied he found the fight stupid and couldn't be bothered about it. Kokoro praised him for his bravery, stating it took a lot of courage to be honest, and said she was too scared to say anything. As Mitsuru walked to leave the greenhouse, Kokoro accidentally dropped the book with banned information she found at the abandoned town. When Kokoro admitted she had kept the book, Mitsuru stated the book didn't involve him and implied he'd keep it a secret. After he walked out of the greenhouse, Kokoro looked at the book and had a sad expression. When Zero Two tricks the boys into walking in on the girls bathing, Mitsuru has no reaction but Kokoro freaks out and hides in the bath while the other girls throw bathroom supplies at the boys. While not stated, it is implied that Mitsuru's bravery of being honest might have given Kokoro the courage to speak up to her fellow pistils to end the fight later on. Ichigo and Ikuno notice this, even commenting on how unusual it was for Kokoro to be so assertive.
Whilst on a special mission to defend the S-Planning facility, Mitsuru collapsed due to child fever and put Chlorophytum out of commission. Kokoro became concerned for Mitsuru upon learning he had a risky injection to become a parasite when he was a child. Even after recovering, testing found Mitsuru and Ikuno's sync rate had dropped so low Hachi noted Mitsuru could become a pruning target. This leads to Nana suggesting the option of a partner shuffle between the members of the squad. Despite promising to be partners with Futoshi forever, Kokoro is uncomfortable with his feelings for her because she doesn’t feel the same. Kokoro volunteers to try riding with Mitsuru, shocking the entire squad, including Mitsuru, and bringing Futoshi to tears. Kokoro and Mitsuru try testing their para capacity and although it is in the lower range, it is stable. However, Mitsuru is indifferent to the arrangement while Kokoro seems content with it.
Later on, Mitsuru finds Kokoro talking to herself and playing with her baby doll in the greenhouse. She jumps when he asks her what she is doing, then they start chatting. Kokoro asks why he thinks humans stopped having children because having a baby was the most natural thing in the past. Mitsuru doesn't care to know why and tells her not to think of unnecessary things, as he says one look at the adults makes it clear they don’t need others to live for, which makes her feel sad. He asks her if she became his partner out of pity but she denies this before the sirens go off. Before boarding Genista, Futoshi tells Mitsuru to protect Kokoro but Mitsuru brushes this off as nonsense. Futoshi gets angry but Kokoro assures him she will be alright and Mitsuru proceeds to board Genista. On their first mission as a pair, they struggle to fight against the Klaxosaur due to Mitsuru’s obsession with surpassing Hiro. Their connection eventually falters due to Mitsuru blindly crashing Genista head-on after failing to eliminate klaxosaurs, hurting Kokoro in the process. The klaxosaur is about to crush them with its foot when Chlorophytum runs in order to protect them, saving them.
Inside Genista, Kokoro asks him to reconnect, but Mitsuru tells her he's incompetent and shouldn't get her hopes up. Kokoro refutes his claim, telling Mitsuru to lean on and trust her more, to which Mitsuru reveals the childhood promise he and Hiro made to pilot together but Hiro apparently broke the promise. He reveals that incident shattered his faith and he can’t bring himself to trust in anyone, fearing his trust will be broken again. Kokoro comforts him, saying she also broke a promise and hurt Futoshi, and she isn't the sweet girl everyone thinks she is. She adds that they aren’t perfect and these things are bound to happen. Hence they shouldn't dwell in the past. Mitsuru asks Kokoro if she means he should forgive Hiro and she says only he can make that decision but she wants to laugh and have relationships with everyone.
Kokoro reaffirms that she believes in him and attempts to operate Genista in stampede mode. Even though Kokoro is getting hurt during the stampede she doesn't stop, even after Mitsuru tells her to stop, wanting to prove Mitsuru's competency. Luckily, Mitsuru intervenes and pulls her off the machine before she can get seriously hurt. As MitsuKoko lay on the floor, Mitsuru looks up at Kokoro and asks how she can trust someone to the point of hurting herself, to which Kokoro smiles sheepishly. Mitsuru smiles back at her, commenting he finds her ‘unbelievable’. MitsuKoko reconnects and their para capacity levels shoot to the maximum. Genista is reactivated and blasts a bigger hole in the klaxosaur to reveal its core. Strelitzia leaps in to land the finishing blow and eliminates the klaxosaur.
Upon returning to the FRANXX hanger, Futoshi berates Mitsuru for his recklessness. Kokoro attempts to intervene but Mitsuru stops her. Futoshi punches him and Kokoro goes to comfort him. Following Futoshi's yelling, Mitsuru promises to protect Kokoro as long as they are together, shocking both Kokoko and Futoshi. Although he makes it sound like he is just saying it to pacify Futoshi, it is implied he really means it.
After this incident, MitsuKoko grew closer. Often seen positioned next to or near each other in most scenes, MitsuKoko back up each other's statements and encourage each other during battle. Most notably, they learned from each other, as observed as Kokoro learning to speak her mind bravely and Mitsuru opening up to and trusting his squad mates. Although Mitsuru didn’t respond to Kokoro’s question over their origins during a trip to the Garden, Kokoro and Mitsuru back each other up against Ichigo that Zero Two and Hiro should be allowed to see each other.
After the first battle of the Gran Crevasse, Squad 13 was on standby at Mistilteinn, awaiting further orders. By this time, MitsuKoko has grown much closer to each other and their conversations are much deeper and serious.
In fact, they are so close that Mitsuru requests a haircut from Kokoro, something which is seen as an intimate gesture between a boy and girl in Japan. Mitsuru admits his guilt for how badly he treated Hiro for something that wasn’t Hiro’s fault and, without this grudge, he feels he no longer has a drive to keep him going. When Kokoro finishes, she smiles and laughs, and he asks if his hair looks weird, and she says he looks handsome. When Kokoro gets up and compliments him for reconciling the misunderstanding with Hiro, Mitsuru compliments her handiwork and says she's very kind. Kokoro is taken aback by Mitsuru's words and seems flustered. Dropping to her knees, she kisses Mitsuru.
Mitsuru is surprised, but he doesn’t push her away. Kokoro realizes what she did and gets embarrassed, apologizing as she ran off.
Later when the girls are bathing at the lake, Miku laughingly asks if they had seen Mitsuru's hair. Kokoro is surprised and Miku smirks at her, asking Kokoro if she cut it. Kokoro giggles awkwardly as she'd cut it herself, to which Ikuno comments she thought it looked good on him and Ichigo agrees.
In the evening, Miku wonders what would happen to them if their food rations stopped being dropped off weekly. Zero Two announces the only choice they'd have then would be to make their own food together. At first, Zorome seems skeptical about whether they can pull it off, but Hiro agrees to Zero Two's suggestion. Mitsuru adds that he remembers seeing some cookbooks in the library, to which Kokoro exclaims perhaps they could do it after all. Everyone happily agrees to Zero Two's suggestion, except Zorome. Kokoro uses her knowledge of plants to make a salad out of edible plant parts while Mitsuru makes a salad dressing using their food rations. When Squad 13 sits down for dinner, Miku tastes their salad and says it's good. Kokoro cheers and smiles at Mitsuru, glad their joint effort worked out.
After the 9's arrived at Mistilteinn, MitsuKoko is seen in the greenhouse again, Kokoro brushing Mitsuru's hair and chatting. Mitsuru says he'll be a bit sad to leave since they only began spending time together after they were left to fend for themselves.
Kokoro smiles and pats his hair before touching the base of his neck, which confuses him. Kokoro explains she read that boys and girls can create new life by joining their bodies together and curiously touches his chest, making a sexual proposition to him.
Gulping, Kokoro unzips Mitsuru's uniform, saying she believes procreation represents hope for them. Mitsuru feels extremely uneasy at this point, so he shoves her hand away, standing up and asking what she's doing. After Zorome walks in on them to remind Mitsuru about water duty, Mitsuru sends Zorome away and asks Kokoro where'd that came from and was shocked to hear Kokoro had been thinking about it for a long time.
Mitsuru later meets Hiro while on water duty. After a chat, Hiro helps Mitsuru realize he is in love with Kokoro. This puts his mind at ease on his feelings and makes him even more determined to support and make Kokoro happy.
Upon returning to the boarding house, Mitsuru and Hiro find the rest of the squad gathered in the living room because Zorome told them about what Mitsuru and Kokoro were doing in the greenhouse. Futoshi then asks Mitsuru if he and Kokoro have kissed. Kokoro blushes, and the squad have gotten their answer. Mitsuru is about to say something but then the 9's come in and ask Kokoro about the baby book. Kokoro confesses to her squadmates that she wants to have a child so she could 'leave her mark on the future'. Since Kokoro hadn't directly told him about this, Mitsuru is shocked and confused. Upon hearing Kokoro's intentions, Nine Alpha calls Kokoro disgusting for trying to defy Papa, their avowed leader. Mitsuru tries to stand up for Kokoro, but not before Ikuno slaps Nine Alpha. This leading to their caretakers to intervene and break up the fight while interviewing Kokoro about rebelling against Papa.
Later that night, Mitsuru waits for Kokoro in the greenhouse but she doesn’t show up. He then finds Kokoro crying in one of the sealed off rooms. Kokoro tries to apologize for trying to force Mitsuru into it and he says she wasn’t but she calls him a liar. She tells Mitsuru to leave her alone, but Mitsuru doesn't want to hear any of that. As Kokoro gets up to leave, Mitsuru says he won’t leave her alone and pulls her into a hug, telling her that he is here for her and she can lean on him more. He tells her not to decide things on her own and expresses his desire to make her happy. As Kokoro cries, she wonders if creating new life is really such a bad thing and if they are allowed to think of their future. Mitsuru chokes back his tears and kisses Kokoro, who pulls him closer.
After consummating their relationship, MitsuKoko is later shown lying naked in each other's arms. Following this, they start meeting in the abandoned room in secret to spend their nights together.
A couple of weeks pass, as Mitsuru wakes up one morning and finds Kokoro looking at the fully bloomed cherry blossom trees out of the window. He stands beside her and notes how beautiful they are, and she agrees.
Before Squad 13 leaves Mistilteinn for the Bird Nest, they decide to hold a wedding for MitsuKoko as suggested by Hiro. After learning what marriage means, MitsuKoko like it and decide to get married themselves. As the squad makes the preparations for the ceremony, Kokoro gets a wedding dress made by the girls whereas Mitsuru makes the rings. He tells Goro what they’re for and Goro says Kokoro will love them, and Mitsuru blushes as he says he hopes so. Later that evening, as everyone paints the house, Kokoro and Mitsuru paint together and pose with their friends for a group picture, with Kokoro holding Mitsuru by the arm. On the day of the wedding, Mitsuru nervously paces below the stairs until he sees Kokoro coming down in her wedding gown. He blushes and shyly looks away. Kokoro links arms with Mitsuru and tells him they will find happiness together, and he agrees.
As they walk down the aisle arm in arm, their squadmates throw sakura petals and ring bells to welcome them. Mitsuru and Kokoro exchange vows and then the rings Mitsuru made earlier and are about to seal their wedding vows with a kiss.
However, the 9’s and an APE assault team crashes the wedding and to take MitsuKoko away for indoctrination. Squad 13 tries to fight back to give MitsuKoko a chance to escape but the squad is outnumbered by APE's soldiers and MitsuKoko are accosted by the 9's. As they are restrained and pulled apart from each other, Kokoro cries out for Mitsuru and he tries to save her before he is knocked out and they are taken away.
Squad 13 are sent to the Bird Nest and wait a couple of weeks for MitsuKoko's return. When Mitsuru and Kokoro do return, the squad's worst fears come true. They realize all of MitsuKoko's memories of each other have been removed. MitsuKoko not only do not remember their relationship prior to the mindwipe, but they also don't even recognize each other and are confused when their squadmates tell them they were FRANXX partners previously because they think the other is a new team member.
Kokoro attempts to partner with Futoshi again but he refuses and insists that she stay with Mitsuru, who accidentally witnessed the argument. After Futoshi walks away, Mitsuru asks Kokoro what were they talking about and apologizes for eavesdropping. She says Futoshi no longer wants to be her partner because he wants her and Mitsuru to team up but both are confused why. They then talk about how their friends keep telling them about what happened to them but both they don’t remember. Mitsuru says he doesn’t think he will develop feelings for her and she agrees. They are later seen talking to each other, supposedly getting to know each other better.
After settling down at the Bird Nest, MitsuKoko take off their wedding rings, puzzling Futoshi. Kokoro gets nauseous from morning sickness and runs to the bathroom to throw up. Ikuno mentions it has been happening a lot lately and Ichigo suggests Kokoro take time off the upcoming mission. Kokoro states Papa sent her back even after erasing her memories, so she must fight to death for him. Miku is shocked and exclaims that none of them belonged to Papa because Kokoro and Mitsuru showed them that they all must leave their mark for the future. However, Kokoro doesn't remember the wedding and is perplexed.
MitsuKoko stands in front of Genista in the FRANXX hangar. Mitsuru enters Genista and reassures Kokoro they will be able to connect since their squad mates state they were FRANXX partners before. Kokoro does not say anything and rubs the base of her finger where she used to wear her wedding ring.
During the 2nd battle of the Gran Crevasse, Mitsuru compliments Kokoro for fighting well and almost calls her by her code number but then calls her by her nickname. By doing so, it triggers a painful flash. The pain and the shock catch him off guard, causing him to disconnect from Kokoro. As Genista struggles to regain control, Kokoro asks Mitsuru what is happening. She calls him by his nickname and gets the same painful flash too. MitsuKoko surmises the pain is caused by saying each other's names. Bewildered and terrified, they shut down their FRANXX, forcing Delphinium to support Genista.
While Genista does not continue in the fight afterwards, it is part of the mission to bring Zero Two to Hiro. Kokoro expresses her desire to keep fighting even if she dies, which concerns Mitsuru. He tells her they need to work with their friends as a team to survive the battle against VIRM rather than going into the fight and readying themselves to die. Although she seems reluctant to listen, she agrees.
Following the battle against VIRM, the parasites are left to fend for themselves with low food supplies and the lack of maintenance. At a meeting, Kokoro seems to keep her distance from Mitsuru, who keeps looking at her with concern. Kokoro then becomes nauseous due to morning sickness and excuses herself. Mitsuru gets up to check on her out of concern but stops himself and the meeting resumes.
The next day, the parasites are working in the fields again when they discover the remains of a klaxosaur and a VIRM soldier which killed each other. Kokoro collapses due to nausea and Miku rushes to her aid. As Kokoro drifts in and out of consciousness, Mitsuru reaches out to Kokoro and calls out her name despite the searing pain in his head.
When Kokoro comes to, she is in a hospital ward surrounded by her squad mates. The new Nana says her urine sample revealed traces of HCG, which confuses Kokoro. The new Nana explains Kokoro is pregnant and cannot pilot a FRANXX anymore. Upon hearing this, Mitsuru realizes he fathered the unborn child and falls to the ground in shock. Kokoro reacts in a similar manner, grasping her sheets tightly. The new Nana recommends abortion as a treatment and asks Kokoro to let her know when she makes a decision on whether to abort or give birth. As the new Nana leaves, Kokoro calls for help out of fear and confusion as she is in a dilemma on what to do next. Mitsuru sits on the floor, shell-shocked, as Miku asks the boys to leave the room.
As the boys walk down the hallway, Mitsuru, guilt-stricken for causing Kokoro pain and unsure which choice is right, stops and asks Hiro what he should do, but Hiro can't answer him. Following this, Mitsuru goes to Kokoro's room in an attempt to talk things out but is too afraid to face her. Later that night, as the squad reflects whether they will find something so important that they will die for it, Mitsuru realizes the importance of being a parent and, feeling a deep attachment towards his unborn child, decides he wants Kokoro to keep their baby. The next morning, Squad 13 leaves for space to help Hiro rescue Zero Two, but Mitsuru and Kokoro stay behind. As Kokoro still hasn’t made a decision on what to do with the baby, she does not join the squad in this mission as she is no longer able to pilot a FRANXX. Mitsuru chooses not to go because, as he tells Hiro, he wants to reconcile with Kokoro, who is surprised.
When Kokoro asks him why he didn’t go with another partner, Mitsuru explains he feels it is his responsibility to take care of Kokoro and their child, to which Kokoro coldly replies he didn't have to. Since they didn't even remember past memories of each other, she says she already told him that she didn't expect anything from him, implying that he had told her his decision to be there for her and the baby earlier but she rejected him. It is worth noting that at this point, Mitsuru and Kokoro seem to have 'swapped roles' in their relationship. Prior to the Partner Shuffle, Kokoro would reach out to Mitsuru and try to comfort and support him in the period when he was struggling to pilot, but Mitsuru would coldly reject her. Now, Mitsuru is trying to reach out to Kokoro in attempt to show support and concern during the time she struggles with the choice of abortion or keeping their baby, but Kokoro rejects his help. Also, prior to the memory wipe, Kokoro was the one who wanted to have a baby to leave a part of her behind before she dies and she came to believe there was more to life than piloting a FRANXX. Whereas Mitsuru initially didn’t believe he needed a reason to live other than to fulfill his parasite duties and he had no interest in anything else. Now, Mitsuru is the one who wants the baby and is willing to do anything for it because he considers the baby as his reason to live while Kokoro is conflicted with what to do and she feels she has no reason to live because she is terrified of losing her place as a parasite If she decides to give birth.
More wounds appear on Zero Two's body and Kokoro struggles to keep up with them. The battle in space intensifies and causes a giant thunderstorm on Earth. Despite this, Kokoro still stays by Zero Two's side despite the ill effects the rain might cause to her body. Mitsuru runs to Kokoro's side and tells her to get inside or she might fall ill and it will be bad for the baby. Kokoro doesn't listen and says she doesn’t care because, since she can‘t pilot anymore, she was pretty much useless and had nothing to live for but she wants to make herself useful by using her body to protect Zero Two. Mitsuru decides to stay with them and she pleads for him to leave her alone and she doesn’t hold him responsible for the baby but he replies he is not trying to be responsible and tells Kokoro if she has nothing, he doesn’t too. He adds, however, he's found his reason to live - to protect Kokoro and their baby's future. Mitsuru takes out his wedding ring from his pocket as proof of his willingness to commit himself to her.
Kokoro asks why Mitsuru still had his wedding ring and why he would still say her name even though it hurt him. Mitsuru replies even though he feels he's a weakling and doesn't really know what 'love' means, he feels that if they're together, they'll be able to keep walking through any challenge and they can start over. He adds that this is their battle and he'll call her name as many times as she wants. She shows him that she also kept her wedding ring. Kokoro cries as they interlock hands and cry out each other's names as they embrace. When the storm passes, MitsuKoko watches Zero Two walk towards the sky and her body turn into a statue.
MitsuKoko are later seen holding hands behind the statue, wearing their wedding rings. This is similar to when they stood behind Zero Two prior to her turning into a statue but they were kept at a distance from each other to symbolize the emotional distance between them over their disagreement over what to do about the baby and Kokoro initially didn't want anything to do with him. But this moment with them standing behind the statue and holding hands and wearing their wedding rings symbolize their reconciliation and growing attachment to each other after Kokoro is moved by Mitsuru’s promise to be there for her and their child. It is also worth noting that, although both initially were ready to move on with their lives by removing their wedding rings and agreeing they would never develop feelings for each other again, they kept the rings likely because they still felt a connection to each other and it felt wrong to get rid of the rings. This implies deep down, both were waiting for each other to reach out and didn’t want to truly forget their past.
Afterwards, Kokoro begins to warm up to Mitsuru and Mitsuru becomes more protective of Kokoro, to a point where Kokoro has to tell him not to worry so much. They start to become excited of their child’s imminent birth.
As Kokoro's pregnancy progresses, Mitsuru is glad when Kokoro receives the treatment needed for her pregnancy, and he finds excuses to spend time by Kokoro's side and at times has to be dragged back to the fields by Zorome and Futoshi.
245 days after Hiro and Zero Two entered the warp gate, Mitsuru rushes to Kokoro's hospital room. Upon reaching, he sees that Kokoro has given birth to a baby girl. Mitsuru is overcome with shock and love for his daughter when he sees her for the first time, and he falls to his knees.
Kokoro refers to Mitsuru as 'papa' and tells their daughter he's here. When their daughter reaches out and holds his finger, Mitsuru is overwhelmed with joy and cries. After leaving the room, Futoshi congratulates Mitsuru for being the first parasite to become a father. Over the next two years, MitsuKoko happily raises their daughter together and this allows them to gradually grow closer to each other. At some point, when Ai was still a baby, she became fussy while Mitsuru held her and Kokoro, who was doing laundry, watched as Mitsuru tried to ease Ai’s cries.
Two years after HiroZero entered the warp gate, MitsuKoko's daughter, Ai, is playing in the field next to Zero Two’s statue. She suddenly hears Zero Two crying out for Hiro and Ai begins saying darling. Mitsuru picks Ai up as she repeats darling again. Kokoro calls Mitsuru "Papa" and tells him it's okay to call her "Mama" because saying her name will cause him pain, but Mitsuru still calls her by name. Ai keep saying "darling" and Kokoro finds this strange because Ai doesn’t know that word yet. Both surmise this means they can communicate with HiroZero in space through the statue.
MitsuKoko calls the rest of the parasites up, joining hands with each other to send their thoughts and prayers to HiroZero. MitsuKoko hold hands while Kokoro holds Ai in a sling.
They tell HiroZero that they had their child and named her Ai, which means love, a word they were never taught. Mitsuru says he read from an old book that the way HiroZero felt for each other means they love each other, and he and Kokoro want Ai to inherit that bond. They proudly look at their daughter and then each other, showing they have grown to love each other again. After HiroZero's sacrifice, Kokoro drops to the ground, crying as she was touched by the sacrifice made. Ai comforts her and Mitsuru kneels down to her side to comfort her too.
Sometime later, Kokoro gives birth to their second child which is a boy.
Eight years after HiroZero's sacrifice, the parasites have a reunion at a school ceremony. MitsuKoko is shown to have three children, with a fourth on the way. As Zorome and Miku argue, MitsuKoko giggles. After the school ceremony, they stand next to each other with the rest of Squad 13, recalling the lessons HiroZero taught them.
While holding hands with Futoshi, Kokoro notices Mitsuru walking alone and she excuses herself to water the flowers. She follows Mitsuru to the greenhouse while he sulks about Hiro and she asks him if he is alright, and he says he is fine. She offers to listen to anything he has to say but he coldly replies he had nothing to say to her and asks her to leave him alone before he storms out of the greenhouse. Kokoro sadly watches him as he walks away.
During the squad’s beach vacation, Kokoro follows Mitsuru into the abandoned city and he asks why she followed him. She asks him to come back to the beach but he declines and asks her to leave because he can’t guarantee her safety if she stayed. She continues following him and he seems annoyed when she explains she is following him because he is always so serious but more so that she is interested in the city. He then notices she wanders off on her own and he finds her in the clinic. He manages to save her from getting crushed by debris by grabbing her to the ground. However, he is shocked to see he is touching her breast, which is exposed from her bathing suit top, causing him to blush intensely and stare. As Kokoro comes to, he backs away while reminding her how dangerous it was to be left alone. She then thanks him while he blushes and he notices the book but doesn’t say anything.
Whrn Kokoro suggests the squad rescue the 9’s from being pruned, everyone is unsure and Futoshi is the most opposed to it, as it would mean going against Papa. However, it is Mitsuru who agrees with Kokoro and he says he has an idea to save the 9’s but he will need their help. Kokoro looks at Mitsuru intently and in an appreciative gaze. After rescuing the 9’s and hiding them in one of the abandoned rooms, Mitsuru warns her that the adults will realize what they did and buying time will be their main issue. Kokoro praises him for suggesting the abandoned room as a hiding spot, but he replies he just wanted to thin of an idea before Hiro. He shows her a photo of the previous Squad 13 and she realizes they were destroyed. This prompts her to say she doesn’t want to live just to die fighting and he says he doesn’t want to either. Futoshi and Ikuno eavesdrop on them, as Futoshi is sad at how close MitsuKoko are getting and Ikuno says it can’t be helped because Mitsuru is the one who said the words Kokoro needed to hear.
The next day, they meet in the greenhouse and Mitsuru catches Kokoro playing with her baby doll, which causes her to jump in surprise. He then notices the baby book and looks through the pages as Kokoro asks why humans stopped having children. Mitsuru says likely because it’s not necessary and looking at the adults makes it clear they don’t need others to live for. She asks him if he’s alright because he looks unwell but he replies he’s fine and they discuss the 9’s. Mitsuru comments that their knowledge of the world is insufficient and she agrees. Shortly after, Mitsuru falls ill with a fever and he asks Futoshi to keep it a secret from Kokoro or else she will worry. He further says that he loves the greenhouse because the flowers help him forget his problems but assures Futoshi that he is not competing with him over Kokoro. Kokoro quickly notices something is wrong with Mitsuru and asks Futoshi, who realizes how worried she is for Mitsuru. Although Futoshi likes Kokoro, he and Ikuno request a partner shuffle and Kokoro is asked to ride with Mitsuru. Kokoro says she doesn’t know if she will be useful but she asks him to ride with her, which he agrees.
During their first battle as partners, Mitsuru becomes angry at Hiro for commenting how he is not well enough to fight. Mitsuru charges Genista at the Klaxosaur despite Kokoro telling him they need to be careful and the Klaxosaur grabs ahold of Genista. The FRANXX deactivates as it is is being crushed and Kokoro awakens. Mitsuru tells her that he will hit the switch button to help her escape because there is no system for both of them to escape and only one person is necessary to kill the Klaxosaur. He sadly smiles as he apologizes for destroying Genista and he never had the qualification to pilot with her, and he says goodbye. Kokoro stops him from pushing the button and she tells him that it’s not impossible, as he can rely on others and she reminds him from when he saved her at the abandoned city. She vows to protect him and starts to pilot Genista ng and it enters stampede mode. As she cries out in pain, Mitsuru pulls her out of her seat to stop her and criticizes her for being reckless. She smiles as she says she escaped from the Klaxosaur because she believed Mitsuru would stop her. This causes Mitsuru to break down as he asks how she can trust someone like that and admits the reason behind his grudge against Hiro. Kokoro understands Mitsuru has been hurt so much he can’t recover but she notes she hurt Futoshi by pairing up with Mitsuru but Futoshi understands. Mitsuru asks if she rode with him out of pity and she says no, and the reason is because she likes him. Mitsuru is surprised and almost speechless, as they are still in a battle. Kokoro says she just wanted to say it. Mitsuru realizes that although it feels strange and he fears he will go back to being a fool and suffer again, his heart feels warm. They reactivate Genista and Kokoro says they will walk the road as partners together, which gives Mitsuru the strength to pilot Genista. As they synchronize, Mitsuru says that becoming one with Kokoro makes living in this world useful and she again asks him to walk together with her. As the battle continues, Mitsuru vows to Futoshi that he will protect Kokoro. After the battle is over, Mitsuru asks Kokoro to cut his hair because he wants to minimize the risk if something goes wrong in future battles but also because he wants to protect her. Kokoro is surprised but then she smiles and starts cutting his hair. Mitsuru admits to himself that he likes everything about Kokoro.
When Kokoro searches for Delta, Mitsuru and Futoshi stop her, saying that she had searched hard enough. But Kokoro doesn't waver, saying that she thought Delta must be feeling anxious when alone. Mitsuru decides to accompany her, which earns an angry shout from Futoshi. Mitsuru says that Kokoro would still go even if they both tried to stop her. Futoshi grudgingly admits that Mitsuru is right and grumbles about Mitsuru's way of speaking because it sounds like Mitsuru knows Kokoro so well.
After hearing about Hiro's story about what happened between him and Zero Two, Mitsuru and Kokoro are shown together in the greenhouse. Kokoro says that the reason Hiro didn't remember the promise is because his memories were wiped. Mitsuru stares at his little finger, his face showing guilt.
When Zero Two is held captive by the Klaxosaur Princess, Mitsuru suggests that he and Kokoro will take Hiro to where Zero Two is, resulting in letting Hiro get into Genista. Mitsuru and Hiro then reconcile and Kokoro feels happy for them.
At the end of the final chapter, as everyone contemplates their future, Kokoro holds Mitsuru’s arm, which confirms their relationship.
In one of the illustrations in the final volume, Kokoro is shown pregnant with their first child.
DARLING in the FRANXX!
In chapter 4, Mitsuru is hospitalized after his sortie with Zero Two and rejects help from the squad. However, when Kokoro brings him flowers, he doesn’t reject her gesture and only grunts.
In chapter 15.5, it is a special featuring the girls giving chocolates to the boys for Valentines Day. This also applies to Kokoro implying she made chocolate for Mitsuru.
In chapter 27.5, it is a White Day special in which the girls find the boys making chocolates for the girls, which could imply Mitsuru is making some for Kokoro.
In chapter 31, Mitsuru gets frustrated at not being able to measure up to Hiro and Kokoro calms him down.
In chapter 33.5, it is a Code 326 Day special and features Mitsuru as the conductor of a band consisting of his squadmates, including Kokoro who seems to enjoy playing.
In chapter 46.2, it is a Code 556 Day special and features Kokoro tending to the flowers in the greenhouse with Mitsuru.
In chapter 47, it is in reference to Kokoro giving Mitsuru a haircut and the boys playing with his fluffy hair, much to his annoyance.
In chapter 52, Kokoro and Mitsuru act as a couple. Hiro and Zero Two introduce the concept of a wedding and the squad begins preparations for their wedding.
In chapter 53, MitsuKoko have anxiety before their wedding; Mitsuru wants to see Kokoro before the ceremony and ignores Goro’s warning it is bad luck by saying it is just a superstition. Kokoro nervously asks Ikuno if it’s okay for her to go through the ceremony.
In chapter 69, the squad decides to take a group picture on how they normally act. Kokoro is thrilled but Mitsuru is reluctant.
In chapter 70, Mitsuru and Kokoro hear Ai repeating “darling”, and everyone sends their prayers to Hiro and Zero Two while cheering for them with light sticks.
In chapter 72, Ai asks Miku to tell her stories about her parents’ childhood and Miku starts off by describing Mitsuru as cold before he tells her to stop, much to Kokoro’s amusement.
In a chapter 77 extra, Mitsuru is shown wearing a flower crown made and given to him by Kokoro.
In a chapter 79 extra, Mitsuru is getting ready to leave for work in the fields but doesn't want to leave Kokoro and Ai, forcing Futoshi and Zorome to drag him with them. MitsuKoko‘s son is then shown taking his first steps.
In another Book-Only extra chapter, the squad (as modern day high schoolers) is walking home, and MitsuKoko are seen walking together.
In the first Drama CD, Zorome dreams of the boys singing Torikago and getting tickets to an XX:me concert. Goro mentions Mitsuru is Kokoro’s fan. In Miku’s dream which is off the boys attending the concert, Mitsuru cheers for Kokoro. Meanwhile, Kokoro blames herself for not stopping Miku from eating a mushroom that makes her fall asleep. Mitsuru assures her that it’s wasnt her fault because Miku always does what she wants. Kokoro notices Mitsuru staring at her and becomes shy. Ikuno teases Mitsuru that he always stares at Kokoro’s thighs after Miku falls asleep on Kokoro’s lap, raising the hem of her uniform. Mitsuru blushes and denies it, and Kokoro is embarrassed. Later, after Ikuno says she will eat a mushroom because she wants to know more about Ichigo, Mitsuru asks Kokoro if she wants to eat a mushroom with him because having a dream, no matter how foolish it is, will bring them relief. Kokoro agrees and they eat two mushrooms and fall asleep. This strongly hints that he wanted to know more about her by having a dream about her.
In the second Drama CD, Mitsuru worries for Kokoro as they suspect a strange creature is in the house. Upon hearing a snake-like noise, Mitsuru tells Kokoro to run with Miku for safety. When Kokoro and Miku are seemingly captured, Mitsuru becomes very alarmed and scared but he attempts to confront the creature before he is caught.
In the third Drama CD, while taking care of Zero Two, who was acting like a baby, Kokoro mentions it will be a while before she can do this again and Miku asks what she means, Kokoro replies it is a secret. Mitsuru mutters it is their fault, implying she is pregnant with his child.
- “Kokoro! Please don't run off alone. I told you, didn't I? I can't guarantee your safety.”
- — Mitsuru, to Kokoro after saving her from falling debris
- “Mitsuru, you can rely on others more, you know. I'll believe in you, so believe in me too.”
- — Kokoro, following the Partner Shuffle
- “I promise... I promise to protect Kokoro from now on.”
- — Mitsuru, to Futoshi following the Partner Shuffle
- “It's funny. Hearing that from you makes me feel like I can do anything.”
- — Mitsuru, to Kokoro after Kokoro gives him a haircut
- “So that's what this is. I... love Kokoro.”
- — Mitsuru, after talking with Hiro about his feelings for Kokoro
- “Let's find happiness together.”
- — Kokoro, to Mitsuru on their wedding day
- “Please don't say you have nothing. If you don't have anything, neither do I! But I've found my reason to live. I want to protect you and that baby's future. I'm a weakling! And I don't really understand what love is, either. But I can keep walking if I'm with you. That's what I've come to believe.”
- — Mitsuru, to Kokoro during the thunderstorm
Series' finale shows Mitsuru and Kokoro have three children (two daughters and one son) and are expecting their fourth child. Mitsuru and Kokoro are shown to be loving and doting parents towards their children.
Ai is the firstborn daughter of Mitsuru and Kokoro. She is also the first naturally born child of Parasites after APE's departure. Ai is the Japanese word for "love" (愛). Mitsuru and Kokoro named her after this in honor of Hiro and Zero Two's relationship.
Ai was conceived when Kokoro admitted her yearning to bear a child to leave a mark for the future and Mitsuru comforted her after she was berated by Nine Alpha, leading to them sleeping together for the first time. Quickly, Mitsuru began to share Kokoro’s perspective on having a child and they began trying to conceive. However, they lose all their memories of each other as punishment for violating the rules on no intimacy between parasites.
Although Mitsuru and Kokoro did not know what to do when Kokoro's pregnancy was first announced, Kokoro decided to keep the baby and Mitsuru was supportive of that because he said the baby had given him a reason to live. Despite the risks of piloting a FRANXX while pregnant because it would cause detrimental harm to the baby, Ai was born perfectly healthy, as this was due to that Kokoro was roughly a month pregnant and quickly got the prenatal treatment needed. Ai was born on January 10th, 245 days after HiroZero left through the warp gate.
When Ai was born, Mitsuru was so overcome with joy at becoming a father that he cried and Kokoro was happy to become a mother. Despite their rough start, MitsuKoko managed to form a loving relationship and take care of their newborn daughter. Kokoro and Mitsuru love their daughter dearly and Mitsuru dotes on her. She greatly resembles her mother, as she has Kokoro’s hair color, but she has Mitsuru’s eyes. As an infant and toddler, her facial features resembled Mitsuru when he was a child.
Ai seems to have telepathic abilities as she was the one who alerted everyone to pray for Hiro and Zero Two in space. When Ai is 18 months old and playing in the fields next to Zero Two's statue when she senses something is amiss. She runs up and pats Zero Two's statue, repeating the word "darling" over and over again, to the surprise of her parents, as she'd never learnt that word before. MitsuKoko surmises the statue of Zero Two is connected to Zero Two in space and call everyone to send their thoughts and prayers to HiroZero.
Ai is a lovable and precocious child who is loved dearly by her parents. She is a kind-hearted little girl, as seen when she comforted her mother Kokoro after HiroZero's sacrifice. In the MATO comic, Ai is also portrayed to be curious and enjoys listening to stories as she asked Miku to tell her stories about her parents.
MitsuKoko had their second child, a son, shortly after HiroZero's sacrifice. He was first seen being carried around as a baby by Kokoro whilst she talked to Miku. He takes after Kokoro in looks - he has the same eye and hair color as her and seems to resemble her in facial features, making him Kokoro's 'guy version'. However, his hairstyle resembles his father’s. In the MATO comic, he is seen learning how to walk while his parents and older sister, Ai, encourage him. During the school ceremony, he sat on his dad Mitsuru's shoulders. His name is unknown at the moment.
MitsuKoko had their third child, another girl, sometime after their second. While her exact age is unknown, she appears to be a toddler in the 10-year time skip. She was seen sitting on Kokoro's lap during the school ceremony, reading the picture book Zero Two illustrated. As her hair and eye colour and facial looks take after Mitsuru's, she is Mitsuru's 'girl version'. Given the significance of sakura in MitsuKoko's relationship, she was likely named Sakura.
10 years after HiroZero entered the warp gate, the parasites have a reunion during a school ceremony. When Ikuno, Ichigo and Futoshi chat, Futoshi mentions MitsuKoko are having their fourth child. As this fourth child is never mentioned or shown later, it’s appearance and gender is unknown.
It is a highly popular ship in the fandom, having entered the weekly top 10 anime ships popularity charts and peaking at first place. It rivals HiroZero in popularity among the fans.
The ship gained much popularity after MitsuKoko's first kiss, entering the top 10 list that week. The ship shot up from 7th place to 1st place the very next week after MitsuKoko consummated their relationship. If pixiv fanart numbers are an indication of their popularity, MitsuKoko has the 2nd highest number of fanarts among the DARLING in the FRANXX ships, behind HiroZero.
MitsuKoko was nominated for Couple Ship of the Year during the Anime Trending Awards 2019 and placed 16th out of 20 ships.
When the ship started is often disputed. Some fans argue MitsuKoko only really started after the Partner Shuffle, while others claimed it started during the Beach Getaway or even as early as Episode 04 when Kokoro became concerned for Mitsuru's wellbeing. Kokoro seems to have started exhibiting an interest in Mitsuru after his sortie with Zero Two, as followed him to the greenhouse out of concern and admitted how she admired his independence and honesty. Whereas, Mitsuru didn’t seem to show any interest in Kokoro until after the Partner Shuffle, in which seeing her hurt herself to prove her trust in him made him smile for the first time and he referred to her as unbelievable.
The Darling in the Franxx fandom is quite divided on this ship. Some have applauded the ship's gradual development, while others criticized it for progressing faster than even the main couple of the show. Many of the ship's critics say they were too young to consummate their relationship and have children at such a young age, while fans say no legal age of consent existed in the post-apocalyptic world of theirs, so they weren't in the wrong. A few even went on to say MitsuKoko's act of rebellion was the first step in rebuilding the world. Other viewers simply dislike it because Mitsuru and Kokoro have completely opposite personalities, hence they didn't seem like a good match. However, MitsuKoko shippers note how their personalities rubbed off each other; Kokoro helped Mitsuru become friendlier and sociable whereas Mitsuru helped Kokoro become more assertive and open with her true feelings.
- It was Mitsuru who found the abandoned city where Kokoro found the baby book that led to her yearning to become a mother and her desire to help Mitsuru with his problems. Because of this, Mitsuru is partially and indirectly responsible for how his and Kokoro’s relationship progressed.
- In the first drama CD, Ikuno points out Mitsuru is staring at Kokoro's thighs when Miku sleeps on her lap. This is implying Mitsuru likes Kokoro's thighs.
- This has become a comic gag in MitsuKoko fanfics and fanart.
- Mitsuru is the only one who knows about Kokoro's baby book and keeps it a secret from the others before the 9's discovery of it. In the manga, he is shown to read it for a short while before returning it to Kokoro.
- During MitsuKoko’s first connecting test with Genista, Kokoro’s negative rates were shown to be high but Mitsuru’s positive rates were fluctuating. However, during their first battle, their paracapacity level shot all the way up to the maximum, the highest both of them had than with their previous partners.
- Kokoro was already pregnant with their daughter at the time of her and Mitsuru’s wedding. But her pregnancy is likely to have been shortly after conception but prior to implantation, as implantation takes place 7-9 days following fertilization. This could explain why APE never detected her pregnancy during the memory wipe or else it’s likely they would have terminated it before returning them to Squad 13.
- Kokoro is the first parasite to give birth to a child naturally in close to a century, and Futoshi proudly declared Mitsuru as the first parasite to become a father.
- Due to feeling pain in their heads after saying each other’s names, Kokoro suggests she and Mitsuru refer to each other as ‘Mama’ and ‘Papa’. However, Mitsuru still tends to call her by her name, as her name is important to him as a reminder of their past.
- Kokoro and Mitsuru were each other’s first kiss and the first pair to consummate their relationship.
- They are also the first pair to get married and start a family.
- Episode 17, which focused on Kokoro’s desire to have a child, aired on May 12, 2018 - the day before Mother’s Day.
- Episode 18, which focused on MitsuKoko’s wedding, aired on May 19, 2018 - the same day as the royal wedding of Prince Harry and Meghan Markle in Great Britain.
- When asked during an interview about the different FRANXX model, Aoi Ichikawa, Mitsuru's seiyuu named Genista as his favorite, to the apparent surprise of Ikuno's seiyuu Shizuka Ishigami who expected him to say Chlorophytum. The interview which was translated into English here was dated February 2, 2018, almost two months before the partner shuffle took place.
- According to Clifford Chapin, the English ADR director, Kokoro was the only person Mitsuru, although brash, always responded to first.
Words & Numbers
- Kokoro and Mitsuru are the youngest parasites to parent a child, as Kokoro was 15 years, 7 months old and Mitsuru was 15 years, 11 months old at the time of Ai’s birth. At the time of her conception, Kokoro was 14 years, 10 months old and Mitsuru was 15 years, 2 months old.
- Kokoro's code number is 556 and Mitsuru's code number is 326. When added together, it gives 882. 882 can be read as "hahani" without the diacritic and can mean "to become a mother". With the diacritic, "hahani" becomes "papani" and can mean "to become a father". This foreshadows the birth and conception of their child.
- With the kanji 反乱 (hiragana: はんらん, romaji: "hanran”), "hahani" also means "rebellion". Consummating their relationship and conceiving a baby were acts of rebellion against APE as Papa had banned any relationships besides FRANXX partners.
- Kokoro’s name means ‘heart’ and Mitsuru’s name means ‘fullness’ in Japanese respectively. Their daughter’s name, Ai, means ‘love.’
- When these words are put in a sentence, you get - My heart is full of love.
MitsuKoko shared many interactions in the greenhouse. The most frequently spotted flowers and plants heavily symbolise and foreshadow their relationship, even in the earlier episodes. They are:
- Celosia, which symbolizes foolishness but devoted affection and attachment. As the Celosia is deep scarlet, this reflects Kokoro’s impulsive but strong affection for Mitsuru.
- Red Lotus, which symbolizes romantic love in reference to their growing feelings.
- Red Hibiscus, which symbolizes gentleness in reference to how Kokoro treats Mitsuru. In western culture, it represents the ideal wife, in reference to their marriage later on.
- Cactus, which symbolizes lust in reference to their sexual relationship, also symbolises maternal love in western culture.
- Cosmos, which symbolizes beauty, peace, and order but it also carries romantic meaning as it tells your partner that the two of you will walk together through life, hand in hand. Also, it is nicknamed the “flower of love”, as it represents a couple’s deepest feelings and walking through life together.
- Delphinium which symbolizes affection and deep attachment.
- Cattleya which symbolizes alluring, in reference to the sexual tension between them.
- Orchid, which symbolizes love, luxury, and strength. In Ancient Greece, orchids represented virility; it was believed if a man ate large orchid tubers, a woman would give birth to a boy but if the man ate small orchid tubers, the woman would give birth to a girl. Because the orchids seen in the series have small tubers, this is a foreshadowing that MitsuKoko‘s first child is a girl.
- Bird of Paradise which symbolizes joy but also faithfulness of a man towards a woman. When the squad goes to space with Hiro to help Zero Two, Mitsuru chooses to stay in earth with Kokoro, even though the latter says he could go on with another Pistil. Mitsuru says that this is his responsibility and he wants to reconcile with Kokoro.
- Purple Lilacs, which symbolizes youth but also represents first love. It is worth noting that Mitsuru wore purple Lilacs on his uniform during his wedding with Kokoro, which symbolizes the fact that Kokoro is his first love.
- Purple Lilacs can also symbolize innocence. In the abandoned room in which MitsuKoko started spending their nights together in, there was a vase of withered lilacs near the window. This symbolises the withering of MitsuKoko's innocence the night they consummated their relationship.
- The presence of Cherry Blossoms during their wedding is in reference to them starting over after their memory erasure, as cherry blossoms symbolize renewal and transience of life.
- A vase of Gardenia which symbolizes secret love, was placed in the infirmary where Mitsuru was recuperating from his injuries in episode 4. It is implied that Kokoro has placed those flowers as she's the only character who has shown any interest in growing plants. Some fans believed this is evidence that Kokoro had been secretly in love with him since the start of the series.
- Gardenia can also symbolize purity, clarity, and dreams. Kokoro wore gardenia on her hair for her wedding day. While it has several meanings, it could symbolize the couple's hopes to leave a legacy behind, and their renewed purpose in life other than just being FRANXX pilots.
- MitsuKoko's relationship has been compared to the Biblical story, Garden of Eden.
- In Garden of Eden, God created a garden of paradise and made the first man (Adam) to tend to the trees of knowledge and life. God then made the first woman (Eve) to be Adam’s companion. Both were allowed to eat all fruit except from the tree of knowledge of good and evil. However, tempted by a serpent, Eve convinced Adam to eat the fruit with her and hid themselves from God, who was angry. Adam blamed Eve but God punished them both by expelling them from the garden and subjected them to harsh penalties: Adam was condemned to labour on the earth for his food and to return to it on his death, whereas Eve was condemned to pain of childbirth. Lest before being expelled from the garden, they ate fruit from the Tree of Life and became immortal.
- In comparison, Kokoro and Mitsuru are raised in a dystopian world but are taught about propaganda of utopia and paradise by APE. They have meetings in the greenhouse to talk about various topics and their innermost thoughts, as it’s the one place they feel comfortable to do so without APE knowing. It is in the greenhouse where Kokoro introduces Mitsuru to forbidden knowledge: romantic intimacy, sexual intercourse, and childbirth. Largely due to their upbringing and isolation, they become physically and emotionally attracted to each other, culminating in their relationship becoming intimate. They rebel against APE by staging a wedding ceremony and conceive a child to leave a legacy. When their relationship is discovered by APE, both admit their part. As punishment, APE wipes their memories of each other but their feelings slowly re-emerge, especially after learning Kokoro’s pregnancy, and they recommit themselves to each other.
Opening & Ending Themes
- In the first OP, Kokoro seems to be looking at Futoshi and Mitsuru seems to be looking at Ikuno, while the rest of the squad looks towards the viewer. Following Episode 11, the OP changes, revealing that Kokoro and Mitsuru are actually looking at each other.
- In the second OP, while the rest of the squad seems have their eyes closed or looking away from one another, Kokoro and Mitsuru are looking at each other and reaching out for each other but are being pulled away.
- The fifth ED shows a shot of Kokoro, with a bewildered expression, being embraced by a boy (Mitsuru). Some fans believe this is foreshadowing for MitsuKoko consummating their relationship and or their memory wipe. This could also foreshadow Kokoro’s confusion why Mitsuru still cares for and worries about her after the memory wipe.
- Another shot in the fifth ED shows Kokoro sitting at the stairway and holding her abdomen, which some fans interpreted as cramps or even morning sickness, foreshadowing her pregnancy. This could also reflect her indecision on abortion or keep the baby.
|SHIPS||het||Delpha • FutoKoko • FutoKuno • HaNa • HiroIchi • HiroMi • HiroZero • IchiGoro • MitsuKoko • MitsuKuno • ZeroMitsu • ZoroMiku|
|femslash||IchiKuno • IkuNao|