Mitsuru and Ikuno knew each other since they were young children living in the Garden but they had very little interactions with each other. They knew each other through their mutual friendship with Ichigo. When they were 14, they were assigned to the same FRANXX squad and, after passing their capacity test, they got paired up with each other. However, they quickly developed a strong dislike of each other. Mitsuru didn’t trust others and tended to mock Ikuno for anything he considered to be a flaw. Ikuno despised the boy-girl pairing system which prevented her from being paired with Ichigo (her love interest) and she loathed Mitsuru‘s cynical attitude.
During their startup ritual, their initial para sync is shown to be in the lower range but it is stable enough for them to successfully synchronize and activate Chlorophytum. Mitsuru was unfazed as Ikuno panted from the initial pain of the synchronization.
During the squad's first sortie, Mitsuru and Ikuno attempt to synchronize but fail as Ikuno isn't able to do it. She pleads for more time but Mitsuru tells her not to bother. Chlorophytum was put out of commission and the duo was ordered to stay behind. Nana later asked what happened Ikuno said she was feeling unwell. Mitsuru asks if they were incompatible, to which Nana says that happens a lot during first times. She adds it's not a reason to split them up, much to his disappointment.
During the first sortie, the squad is cornered by a horde of klaxosaurs and Hiro is declined to ride with Zero Two to save them, Mitsuru volunteers to ride with her but Nana is hesitant because he won't be able to handle Strelizia. He persists on the rationale that the others will die but Zero Two refuses until Hiro reluctantly tells her to go with Mitsuru. As he leaves, Mitsuru reveals he just really wants to prove he can pilot Strelizia better than Hiro. During the battle, he becomes empowered by the experience and reveals his amazement that changing partners could make such a difference. He blames Ikuno for their incompatibility by saying he knew he wasn’t the problem and parades how Zero Two is a better partner and that he wouldn't mind being her official partner, which deeply upsets Ikuno. At the end, he is left severally wounded and traumatized.
While Mitsuru is in the hospital recovering, Ikuno is still upset by his words and that she couldn't pilot. Ichigo assures her to be there for Mitsuru as his partner. When a klaxosaur appears, Mitsuru attempts to get out of bed to join the fight despite being wounded and Ikuno tells him not to but he doesn't listen. She offers to help him but he refuses and ends up collapsing in her arms. She helps him up and they get into Chlorophytum. He says he hope she can activate it with him and she tells him not to worry. Thinking of Ichigo, she is able to synchronize with him and they activate Chlorophytum. During the squad’s mission to defend the kissing of Plantations 13 and 26, Ikuno reminds Mitsuru of what they need to do for a successful strategy to reach the klaxosaur’s core but he retorts she didn’t have to tell him.
During a vacation to the beach, Ikuno keeps to herself and reads while the others swim. Mitsuru asks her if she came just to read and she retorts she doesn’t have to force herself to do what the others do. He then comments how happy Hiro has been acting even though he had been depressed recently. Ikuno tells him to keep his thoughts to himself and he mocks her that he was talking to himself, and he tells her that he found an abandoned city nearby.
A few days later, when a klaxosaur sprouts mysterious goo all over the FRANXX units, the goo falls into the cockpits and onto the girls, causing their suits to melt. Mitsuru has no reaction other than a small tint of blush and looks away as Ikuno is exposed. When the girls find out what happened, Ikuno freaks out and tells Mitsuru not to look at her but he says not to mind him because he isn't looking. After the mission is over, she glares angrily at him but he simply walks away.
During the Boys vs Girls conflict, Ikuno goes along with it because she finds the gender separation favorable but he is not interested in the feud and finds it stupid. When the girls split the house apart, Ikuno glares at Mitsuru, who is unfazed and finds the fight to be stupid, but he does nothing to defuse it. When Zero Two tricks the boys into walking in on the girls bathing, Mitsuru has no reaction but Ikuno freaks out and, along with the other girls, throws bathroom supplies at the boys. When the boys and girls later reconcile, Mitsuru and Ikuno look at each other but he walks away while she smiles, implying they don’t need to apologize or shake hands like the others did because they understand they need to be amicable for the sake of their duties.
Shortly after, during a briefing, Hachi reports that Mitsuru and Ikuno's sync rate has fallen, along with their killing numbers, which Mitsuru attributes to him feeling unwell. While guarding an S-Planning facility, Chlorophytum deactivates and Ikuno finds Mitsuru suffering from a high fever, causing her to worry about him. While he is recovering, Ikuno reveals to the others that his health has been fragile due to that he underwent an Elixir Injection when he was a child. Upon recovering, they undergo a capacity test, which shows their paracapacity rate has fallen lower and, as it is shown that Mitsuru is the source, Nana proposes the squad try a partner shuffle. While everyone debates, Ikuno agitates Mitsuru by telling him to stop acting cool and he knows what caused this mess. He asks what she is talking about and she tells him to drop the act, as it takes courage to face up to others and himself. He asks what her point is and she says he wants to be acknowledged by Hiro, not Papa and the adults. He shouts at her to shut up, causing a scene and everyone looks at him. Mitsuru looks down, ashamed for making a scene. Ikuno smirks and says it suits him better than acting cool and aloof before adding she isn’t like him. After everyone discusses it, Mitsuru looks at Ikuno as she asks to try riding with Ichigo, who is surprised and hesitant but agrees. Kokoro then asks to try with Mitsuru, which surprises everyone. While testing their paracapacity, Ikuno and Ichigo fail to connect and time out whereas Mitsuru and Kokoro manage to maintain a low but stable connection. Because of this, Kokoro is paired with Mitsuru and Ikuno is paired with Futoshi. While in the hallway, they run into each other and she frowns as she tells him he can laugh at her but he doesn't respond.
In the manga, Ikuno shows deep concern for Mitsuru as he starts to come down with a fever and she shows an interest in his budding relationship with Kokoro. While looking for him, Futoshi tells her that he is at the greenhouse with Kokoro and Miku says those two have been acting strange. This intrigued Ikuno. After a battle and his condition worsens, Ikuno tells him to go to the infirmary but he refuses and tells her to leave him alone because he doesn’t want to bother her with his problems. Then he collapses and Ikuno rushes to help him. As he is taken tended, Ikuno learns from Alpha that Mitsuru had an Elixir Injection when he was a child. This shocks her because it has a high mortality rate. Mitsuru asks Futoshi to keep his illness a secret from Kokoro so she won’t worry, which catches Ikuno’s attention. Noticing Kokoro’s concern for Mitsuru, Ikuno and Futoshi’s approach Hachi for a partner shuffle, as both believe Kokoro and Mitsuru can help each other.
During the first sortie following the partner shuffle, Ikuno and Futoshi use Chlorophytum to protect Genista from being crushed by a klaxosaur and to give Kokoro and Mitsuru time to talk out his problems..
Following the partner shuffle, the two slowly became more civil with each other, likely because they no longer had to put up with each other while piloting together. Overtime Ikuno notices a change in Mitsuru's demeanor following his partnership with Kokoro, how he went from a sarcastic and stoic person to smiling and interacting with everyone more. What catches her attention the most is that his hair was suddenly cut shorter and Kokoro confirms she cut it, and Ikuno admits she thinks it looks good on him. This makes Ikuno suspect that Mitsuru and Kokoro have developed a romantic relationship. When this is confirmed after Zorome reveals he caught the two in a compromising position (Kokoro attempting to unzip his uniform to initiate sex with him), Ikuno admits she isn't surprised at all. Nine Alpha shows the squad the baby book Kokoro has been hiding and berates her for wanting to have a baby because humans have cast their gender aside for evolution and is a nuisance. This deeply angers Ikuno and she slaps Alpha, surprising everyone.
A few days pass, and when Hiro announces Kokoro and Mitsuru have decided to get married before they all have to leave for the Bird Nest, everyone is supportive but Ikuno is sullen. During a talk with Ichigo, Ikuno admits she didn't lash out at Alpha to defend Mitsuru and Kokoro but that his words offended her because she is in love with Ichigo. The next day, before the wedding begins, Ikuno gives Kokoro a bouquet of flowers and pins some flowers on Mitsuru's uniform, and they both thank her and she goes to sit in attendance as the wedding starts. However, the 9's and an APE assault team interrupts the wedding and takes the two away. A couple of weeks later, Ikuno and the others are devastated to learn that Mitsuru and Kokoro’s memories of each other have been altered, and Ikuno is upset the wedding they all worked so hard on was ruined. Mitsuru is implanted with fake memories in which Ikuno remained as his partner. To keep Mitsuru and Kokoro as partners, Ikuno and Futoshi decide to remain paired up. She is also worried they will never regain their memories when Papa explains why he ordered the memory erasure and it is impossible to return the memories.
A few days later, Ikuno and the others are shocked to learn that Kokoro is pregnant with Mitsuru's child. Two days later, just before she and the squad leave for space to rescue Zero Two, Mitsuru announces his decision to stay behind so he can be there for Kokoro. Ikuno is seen behind him, smiling as he tells this to Hiro, showing that she is very supportive and proud of him and his choice to be a father to his unborn child and to protect Kokoro. She later becomes very supportive of Mitsuru and Kokoro’s decision to keep the baby after they reconcile. Eight months later, she is present for the birth of their daughter, Ai, and she happily smiles as Mitsuru meets and bonds with his newborn daughter.
When they reach adulthood, it is shown they are still friends. This is evident when Futoshi tells her that Kokoro and Mitsuru are expecting their fourth child, and Ikuno replies she heard.
Prior to the squad’s first sortie, Mitsuru finds Zero Two and begins bad mouthing about Hiro before he proposes he pair up with her. He tells Zero Two that Ikuno is incompatible with him and blames her for the incompatibility but Zero Two rejects him. When Mitsuru does offer to pilot with Zero Two when the mission goes wrong, Ikuno is surprised but doesn’t say anything. Hiro’s resolve to continue piloting with Zero two and Nana giving her approval leaves Mitsuru disappointed.
When a mission goes wrong with Delphinium being absorbed, Mitsuru blames Ikuno that the mission failed and that Chlorophytum malfunctioned because she freaked out. As she is worried about Ichigo being absorbed by a klaxosaur, Ikuno agrees and starts crying. Mitsuru starts to back down as he sees her cry and shifts the blame of the mission failure to Zero Two for acting out against orders.
Ikuno starts to show deep concern for Mitsuru as he starts to come down with a fever and she shows an interest in his budding relationship with Kokoro. While looking for him, Futoshi tells her that he is at the greenhouse with Kokoro and Miku says those two have been acting strange. This intrigued Ikuno. After a battle and his condition worsens, Ikuno tells him to go to the infirmary but he refuses and tells her to leave him alone because he doesn’t want to bother her with his problems. Then he collapses and Ikuno rushes to help him. As he is taken tended, Ikuno learns from Alpha that Mitsuru had an Elixir Injection when he was a child. This shocks her because it has a high mortality rate. Mitsuru asks Futoshi to keep his illness a secret from Kokoro so she won’t worry, which catches Ikuno’s attention. Noticing Kokoro’s concern for Mitsuru, Ikuno and Futoshi’s approach Hachi for a partner shuffle, as both believe Kokoro and Mitsuru can help each other.
In the first Drama CD, Ikuno teases Mitsuru in front of Kokoro by noting how he stares at Kokoro’s thighs, causing him to deeply blush and adamantly deny it. Later, Ikuno decides to eat a mushroom that makes the others fall asleep and have strange dreams. She explains she wants to know more about Ichigo by eating a mushroom and begins meticulously reciting how Ichigo bathes and sleeps. Although he finds this weird, Mitsuru admits he can’t say he doesn’t understand what she means and proceeds to ask Kokoro to eat a mushroom with him. This strongly hints that Ikuno gave Mitsuru an idea to know more about Kokoro via having a dream.
In the second Drama CD, when the squad suspects a strange creature is in the house, Mitsuru becomes scared upon Kokoro and Miku being captured and runs to where Ikuno and Ichigo are hiding. He decides to confront the creature but he is caught and left unconscious, which makes Ikuno worry for him but he makes her run away for her safety.
In the third Drama CD, two years after HiroZero leave for space, Mitsuru helps move research supplies into Ikuno's office and saves her when a stack of books almost fall on her. She thanks him and mentions how she is going to ask for Dr. FRANXX's research files. He advises her not to push herself despite the advances her research may have. Ikuno laughs and wonders why they are human. She then mentions all the things that happened to Mitsuru and now he is a father. She admits she is happy for him for having someone he loves and he is moving on with his life. Mitsuru asks her about herself and she says she has chosen to surrender herself to her accelerated ageing process, but she intends to live as long as possible with everyone else. This shows that the two have truly reconciled and become genuine friends.
This shipping is not very popular due to Mitsuru and Ikuno's mutual dislike for each other, and the fact that both have other love interests. It has been speculated that the reason why Mitsuru and Ikuno failed to synchronize was because of their different orientations (Ikuno wanted to pilot with Ichigo and Mitsuru preferred piloting with anyone but Ikuno). Even when the two reconcile, the shipping failed to progress, especially following the pairing of MitsuKoko and then IkuNao. Many MitsuKuno shippers ship them only because they were partners, like FutoKuno and HiroMi.
- Mitsuru's English voice actor, Bryson Baugus, is a MitsuKoko supporter whereas Ikuno's English voice actress, Leah Clark, likes both MitsuKoko and IchiKuno.
- During their first connecting phase with Chlorophytum, Mitsuru’s positive rates were shown to be in the medium range but Ikuno’s negative rates were shown to be low.
- According to Ichigo, Ikuno may be the only person who understands Mitsuru the most, due to both having personal problems they feel they can't talk to anyone about.
- Despite their disdain towards each other, they do share similar interests and characteristics: they both enjoy reading, prefer to be aloof, have cynical attitudes but hidden soft sides, and wanted to pilot with someone of the same gender but never got the chance to. In addition, both have suffered health issues; Mitsuru had been ill for most of his childhood due to his Elixir Injection but he became healthier as an adult, whereas Ikuno was shown to be healthy until she overused her strength and opted to retain her accelerated health process, causing her to be sickly and bedridden.
- In the first OP, it appears Mitsuru is looking at Ikuno who is looking at the camera. However, after episode 12, it turns out he is actually looking at Kokoro.
|SHIPS||het||Delpha • FutoKoko • FutoKuno • HaNa • HiroIchi • HiroMi • HiroZero • IchiGoro • MitsuKoko • MitsuKuno • ZeroMitsu • ZoroMiku|
|femslash||IchiKuno • IkuNao|