Hiro and Zero Two met when they were small children and living in the Garden. Zero Two was kept isolated at the lab, a facility Hiro often frequented due to his 'child genius' status. Zero Two was the specimen of a ghastly, inhumane experiment conducted by Dr. FRANXX to observe her klaxosaur abilities. Hiro first noticed her when she was being dragged to a room to be experimented on, and he was intrigued by her red skin and horns, but even more so by her battle against the adults when they attempted to confiscate her picture book but she fought back to keep it. Up to that point, he felt he was the only one fighting that battle against authority and was amazed to find someone like him. He felt a deep desire to see her again but every time he tried to sneak away, he was caught. One day, he was leaving the lab after a checkup and heard her scream in pain. Following her screams, he witnessed the horrific experiments she was forced to go through and he begged the adults to help her but the adults replied it wasn’t his business.. The frustration by the adults ignoring Zero Two’s suffering, his desire to learn more about the outside world, and confused why the adults never answered his questions made Hiro determine to rescue her so they could explore the outside world together.
When Hiro was around nine years old, he found the room in which Zero Two resided and hatched a plan to rescue her. Breaking the glass to free her, Hiro and Zero Two ran away from the garden in the snow. Zero Two was initially aggressive towards him due to her lack of trust in others but Hiro understood she didn’t understand what he was saying. Hiro introduced himself first by his code number and than his name, and he wondered what her code number was. Seeing it was 002, Hiro tried to think of a name. He thought of Oni but decided against it and suggested Zero Two but he thought that wasn’t good either. Zero Two tried pronouncing her name but couldn’t. Hiro suggested they go somewhere far away.
Hiro made her shoes from cloth wrappings and they ventured throughout the area. Zero Two recalled how Hiro helping her escape was her first experience of the outside world and, while she didn’t understand his words, she knew he called to her. She saw things with him and walked with him, and every moment they shared was so much fun. As they continued running away, they sat in front of a tree and Hiro gave her first piece of candy, which she loved with delight. She then trusted him enough to show him her picture book and he began reading it to her, as she didn’t understand the words.
Then, a pair of adults appeared, looking for them, and revealed they were ordered to kill Hiro if necessary to capture Zero Two. Hiro then promised to protect Zero Two. The two then resumed running away before the two rested in front of a tree. Hiro tells her the meaning of marriage and she smiles at him for the first time. When they decide to resume walking, Zero Two hurts herself and Hiro bends down to treat her wound by licking her blue blood. As he kneels before her, Zero Two misinterprets his actions as Hiro wanting to marry her. Hiro smiles and says once they get out of the Garden, he'll marry her and become her ‘darling’, moving Zero Two to tears. The two then looked up as Hiro realized they were sitting in front of a mistletoe tree. Zero Two recalled that she came to believe she go do anything as long as she was with him.
Right in front of them, the adults find them and surround them. Hiro tries to protect Zero Two but gets hit on his head and falls unconscious. Hiro would later wonder why he couldn’t protect her because he was a child who didn’t have the power to protect anyone. Zero Two cries and screams for her ‘darling’, as they are taken away to have their memories erased. While Hiro's memories were successfully erased, Zero Two's weren't completely due to her determination to hold onto her memories of him. Hiro was sent back to the Garden and Zero Two was sent back to her room. As such, Zero Two tried holding onto her memories after recalling familiar actions, such as the way Hiro referred to himself with the word "boku", the way he licked her wound, and she learned not only her name but the word ‘darling’. Zero Two felt resentment towards herself for neglecting to see that she and Hiro were different creatures with different blood colors. Since then, she vowed to reunite with him, no matter what it takes, no matter how many people she needs to use as a stepping stone to get to him.
About five years later, when Hiro is 14-years-old, HiroZero get their first glimpse of each other when he sees her aircraft above as it arrives at Plantation 13 and she looks at the window. They later first meet at the lake in Mistilteinn while Zero Two was skinny-dipping. When he rushes into the water after she goes underwater, she jumps out with a fish in her mouth and he is shocked to see a naked girl for the first time. However, Hiro says between seeing her naked and her two alluring horns, he felt like he had been put under a spell so transfixed that he couldn’t take his eyes off her. Zero Two simply walks past him after inspecting him. He asks her if she is a parasite. She wondered why the water doesn’t taste salty like an ocean, which he explains the lake isn’t an ocean. She asks him if he going to swim because of how he was staring at her but he says he thought she was drowning and jumped in to save her. He then shyly asks her to put clothes on. Zero Two calls Hiro a "pervert" for holding her underwear, which deeply embarrasses him and she laughs. She thanks him for jumping in to "save" her. They chat for a bit as Zero Two gets dressed, and she asks him if he is a parasite. He replies no because he can’t pilot and he dragged his partner down with him. She says they are the same because she is always alone thanks to her horns and suggests that if he doesn’t have a place to belong, build one; if he doesn’t have a partner, find one; if can’t find one, take one by force. She pushes him into the lake and licks him, commenting he tastes like danger and says she has taken a liking to him. She asks him if he wants to be her darling, which confuses him. She says his ability is just dormant and she offers to help him awaken it, as she offers her hand out to him. Before he can take her hand, her partner and a group of officers come to take her away. Her partner warns Hiro to stay away from her because she is not an ordinary pistil. Hiro asks what her name is. She replies her code number is 002 but is called Zero Two.
The next day, a klaxosaur attacks and Strelizia, piloted by Zero Two, crashes near Hiro. Her partner dies from his injuries and Zero Two is ready to keep fighting despite being injured and Hiro’s protests. He tries to stop her but she slaps him away. He warns her that she will die but Zero Two says she isn’t afraid of dying and everyone in the plantation will die if she doesn’t get back to fighting the klaxosaur. He then asks to pilot with her to prove his worthiness as a parasite. Zero Two reminds him that he will probably die but he says he doesn’t have a place for himself and he is better off dead if he can’t fulfil his purpose as a parasite. Seeing his tears and commenting how it’s been a long time since she saw a human cry, Zero two relents by smirking and pulls him inside the cockpit, wanting to get a taste of him because he is now her darling. She kisses him and Strelizia is activated. Afterwards, Zero Two pulls an unconscious Hiro out and announces she has found her darling.
The next day, Ichigo warns Hiro not to pilot Strelizia again because of the rumors of Zero Two’s partners dying after three sorties but he says he wants to be sure if he can pilot and if he can’t, he is better off dead. Zero Two visits Mistilteinn to eat breakfast with Hiro, who doesn’t recall what happened and he is slightly uncomfortable when she sits next to him. He asks her if he piloted, she assures him that he did pilot a FRANXX and calls him ‘darling’, which surprises everyone. Nana takes Zero Two back to the city and warns her to stay away from Squad 13 because they are not equipped to be around a pistil like her. Zero Two, however, ignores this and proceeds to watch Hiro as he trains. For Hiro’s mock battle, Zero Two offers to be his partner but Ichigo asks and Nana prefers Ichigo over Zero Two. Although disappointed, Zero Two tells Ichigo to take care of Hiro, which makes Ichigo irritated. However, after a seemingly successful synchronization, his connection with Ichigo falters and she asks what Zero Two did earlier that worked. He brings up the kiss and she proceeds to kiss him but he says he feels nothing. Hiro later tells Goro that he has decided to continue piloting with Zero Two because she is the only one compatible with him and he doesn’t care about the rumors about her regarding her partners never pilot with her more than three times because they die.
After training, he finds her sitting alone and stares at her horns, and she calls him a pervert. She takes him to a balcony with a view of the city. Hiro is amazed, as he has never been in the city but Zero Two is indifferent. She jumps and walks on a thin post, and Hiro worriedly calls her to come back, as it isn’t safe. She tells him that they and everyone else will only become a statistic once they die and they will never be remembered, and calls the city lifeless. She offers to get him out but then jumps back to the balcony, jokingly saying she is kidding.
During the squad’s first mission, most of the parasites are surrounded by klaxosaurs and Zero Two and Hiro are denied going to save them. Mitsuru offers to go with Zero Two since Hiro is not an official stamen yet. Hiro reluctantly agrees and Zero Two, dismayed, walks quietly away from him. Seeing Zero Two about to get in Strelizia with Mitsuru makes Hiro feel a strange sensation and it makes him realize how much he wanted to pilot with her, along with his disappointment that Zero Two didn’t oppose him.
After the battle, Zero Two declares only Hiro is fit to be her darling and Mitsuru is left gravely injured. While recovering, Mitsuru pleads with Hiro not to ride with her because she will devour him. Hiro doesn’t know what to do and sees Zero Two in the docking lounge with Strelizia, which causes him to remember what happened to Mitsuru and her previous partner. Hiro hides from Zero Two when she looks his way but she then walks away.
While he is bathing, Zero Two surprises him and corners him, asking him to run away with her and not worry about the others because he is the only one who can be her partner. He stares at her horns and gulps. She asks him if he is like the others and he thinks she is a monster but the alarms go off before he can respond. A klaxosaur then attacks and HiroZero watch the fight unfold in the control room. Both wonder why they weren’t sent and Zero Two asks about the military officers who have arrived. Nana reveals Zero Two has been ordered to be sent to the front lines alone. Zero Two initially resists but relents to leave and tells Hiro that she believed they could be together. She gently bumps her horns against his forehead as a gesture of farewell and leaves. Hiro asks Nana if Zero Two isn’t human and about the rumors, but she explains Zero Two is no ordinary pistil.
Retorting that she is a normal girl, Hiro disobeys Nana and rushes to stop Zero Two from leaving. As she continues leaving, Hiro admits he is still afraid of piloting with her but being able to pilot with her made him happy and she gave him a reason to live, which is to be her wings. Zero Two then beats the officers and co fronts Hiro about his sincerity. She is amused because no one has said such embarrassing things to her before and takes him to Strelizia so they can head to the battlefield. Hiro wonders if he can pilot but she assures him he can. Despite being warned by Nana for disobeying orders, HiroZero activate Strelizia. Hiro is overjoyed he is piloting and Zero Two compliments him.
Days later, Zero Two surprises Hiro when she arrives at Mistilteinn and asks him to sit with her during breakfast. She offers him a honey-soaked toast and he shyly accepts as she hand feeds him. Hiro later shows her around Mistilteinn and he mentions it can still rain despite there being a glass ceiling above the area. Interested, she asks him to make it rain, but he says he can’t. When asked why she wants him to show her around, she announces she will be living with him. Zorome is disgusted with Zero a Two being in the boys’ dormitory and Hiro takes Zero Two by her hand to leave. During a briefing with Squad 26, Nana informs the others that Papa has given permission for Hiro to rise Strelizia with Zero Two for the upcoming battle. Zero Two is indifferent to Squad 26’s disdain towards her and Hiro promises to keep her under control. When Goro finds out Hiro has a tumor on his chest as a result of piloting with Zero Two, he asks Hiro to stop but Hiro refuses. Similarly, Ichigo asks Zero Two not to go hard on Hiro or else she will kill him, and Zero Two replies it is Hiro’s decision to ride with her and him dying is no big deal.
The next morning, Hiro and Zero Two bump into each other at the lake. Finding the tumor but commenting how beautiful yet painful it is, Zero Two offers Hiro a choice to not ride with her a third time but he insists he will. Before going to fight, she asks him if he is ready and he affirms he is. During the battle, Hiro is growing exhausted as he and Zero Two watch the battle from afar. She comments how Squad 13 is barely hanging in there. He asks her why she fights, as it appears she enjoys it. She isn’t silent momentarily and replies she is probably just a monster, which surprises him. She’s hen asks him why he fights and he replies to protect Papa and the adults, as it his purpose in life. Zero Two calls his response lame and suggests they head intoned battle.
While fighting, Hiro slowly starts succumbing to his illness and almost loses his connection with Zero Two, who asks him if he is done but he refuses to give up yet. After seemingly landing the final blow to the klaxosaur, Hiro is exhausted and nearly consumed by his illness, falling to the floor and severing his connection to Zero Two. Thinking he is dead, he has a vision of Zero Two standing in front of a mistletoe tree and apologizes to her but she ignores him and walks away. As he wakes up, he sees a mentally unstable Zero Two ad she fights in stampede mode and is getting injured by the klaxosaur. Hiro asks himself why can’t he help her and this strengthens his resolve to never run away, allowing him to survive.
Hiro gets up and comforts her from behind, saying he says he is her partner and his wings exist for her. They reconnect and land the official killing blow on the klaxosaur, later walking out of the cockpit together.
After this, the two are made official partners, which makes Zero Two happy. However, Dr. FRANXX warns Hiro not to let her consume his emotions. During a trip to the beach, Hiro and Zero Two swim together and she tells him that this is her first time swimming and tasting ocean water. He blushes as he see some her in her bathing suit, which she notices and asks him why is he staring. He embarrassingly comments how good she looks in it. She brings up that he saw her baked once before but he retorts he didn’t mean to. She pulls herself against him and licks his cheek, happily affirming how his taste makes her heart race. She proceeds to explain that a kiss is a declaration that a person belongs to you and should be shared with someone special. She asks if he has done it with anyone other than her but he is dragged underwater by the boys before he can reply. Everyone notices how happy Hiro has been since he met Zero Two.
During a mission, a klaxosaur spills goo all over the FRANXX units and it causes the girls’ parasite suits to melt. When Zero Two’s suit starts melting, Hiro is deeply embarrassed and, after killing the klaxosaur, he tells her that she is being exposed. While the other girls are angry, Zero Two is undeterred and Hiro unintentionally makes things worse by mentioning that Zero Two said parasites are better off being a little pervy. During the Boys vs Girls conflict, Zero Two isn’t interested in participating and spend some timing fawning over Hiro, which irritates the other girls. Hiro feels forced to do so but he spends the time with Zero Two. He notes the fight is getting out of hand, but Zero Two decides to spice things up by tricking the boys into walking in on the girls bathing. Following that, she steals their clothes and leads Hiro on a chase throughout the house. On the roof, she throws the clothes at him, which makes him laugh. He asks her why she did it and she replies she wanted to take part in a human fight. She falls from the roof, which makes him worried but then he is relieved when she safely lands on the ground. During a talk with the boys later, Hiro says Zero Two seemed so human and it made him more determined to get to know her and take care of her.
When Squad 13 receives their annual presents from Papa, Hiro gifts Zero Two Naomi's mirror as he didn't want her to feel left out. After staring at it for a while, Zero Two jumps and hugs Hiro, thanking him for the gift.
Over time, Zero Two began acting distant with Hiro and speaking less to him, which concerned him. Prior to going to the city for a medal ceremony, he sees her gloomily staring off and he asks her what is wrong but she says nothing. He later asks her to be more open with him because he wants to understand her but she stops him and says they only need to understand each other when they pilot Strelizia. During a battle, Zero Two goes rogue and Hiro has to restrain her from putting themselves in danger. Afterwards, she hugs him from behind and tells him not to worry because they will be together until they die. Her behavior becomes increasingly disturbing and she even begins refusing to listen to Hiro when she disobeys orders.
After being sent to the Garden to undergo tests, Hiro finds her trashing the library to look for a picture book. He asks her to tell him if anything happened, as he is her partner. She asks him to kiss her and corners him against the wall. As she leans in, he sees her fangs and becomes scared, which she notices and backs away, and tells him never mind. After returning to Mistilteinn, Hiro finds her sitting at a lake and is worried when he sees that she has bitten off her nails and tries to tend to her but she again rejects him. Frustrated with her, Hiro confesses that what she is and her past don’t matter to him because he is attracted to the person she is and, after realizing what his feelings mean, he says he loves her. Zero Two coldly offers to show him what goes beyond kissing by unzipping her uniform and shoving him to the ground to try and have sex with him. Hiro rejects this because that’s not what he means. She calls him nothing but her fodder, which saddens him. During a battle, she becomes violent and more rogue, and she reveals she needs to kill more klaxosaurs to become human but he says that’s not possible. As he tries to stop her from losing control, she resists and begins strangling him. She says she will become human so she can find her darling from before. This causes him to connect deeply into her consciousness and recall his forgotten memories.
With tears in his eyes, Hiro mentions this to Zero Two and she begins crying as she realizes Hiro is her long-lost darling and becomes remorseful for her actions. Ichigo bans Zero Two from seeing Hiro after what she did. Zero Two is kept in her room by the squad as she pleads for them to let her see Hiro. She finally becomes frustrated to the point of being physically violent but Goro convinces Ichigo to let Zero Two see Hiro. But when they find he escaped from his hospital room, Zero Two thinks they tricked her and attacks them in a fit of rage. Hiro later finds his friends hurt and Zero Two strangling Ichigo. He calls her a monster and Zero Two, seeing this as punishment, decides to leave for good. Hiro, however, is despaired at her departure and attempts to stop her before Ichigo stops him and kisses him, and confesses her love to him.
During the siege of the Gran Crevasse, Hiro sees Zero Two pilot Strelizia in stampede mode and becomes concerned as she appears to be losing her sanity. Dr. FRANXX asks Hiro if he finds her more beautiful and proud than anyone like a klaxosaur, and Hiro replies she is a normal girl. He returns to Mistilteinn and finds her room destroyed, along with the mirror he gifted her. He gasps when he sees it in its broken, taped-up state. Hiro wonders why he is hesitating to help her and abruptly rushes into the battle, realising he needs her because without her, cants do anything.
Ichigo reluctantly helps him and she sees his mind is full of nothing but Zero Two. Upon reuniting, Zero Two is trapped within her unstable mentality. Hiro connects with her consciousness and sees how much she struggled to never forget him, and pledges to be there for her no matter what. When she regains her composure, she pushes Hiro away because she is a monster and called him a fodder but he retorts he called her a monster and they are even. She says she is a monster but Hiro disagrees.
He tells her they can see the world together now and kisses her. They reconnect and Zero Two confesses her love to Hiro, and he confesses his love to her as Strelizia evolves and neutralizes the klaxosaur.
They begin an official relationship and spend all their time together as the squad is left to fend for themselves at Mistilteinn. Zero Two begins rewriting her old picture book and Hiro visits her at night to see her drawings. He comments its a sad story but she says it was her first pretty thing and she wanted to have something beautiful with him when they were children. She moves his bangs and sees he is growing small horns as a result of ingesting her blood when they were little. They kiss and she says she knows what it means to be human. They later attend Kokoro and Mitsuru’s wedding, which is ruined by the 9’s and the couple’s memories are erased. Hiro and Zero Two are angered and decide to finally rebel against Papa, who promises to free all the parasites in exchange for their cooperation in the final battle.
During the first battle, Hiro and Zero Two reaffirm their promise to be together forever. However, the klaxosaur princess forces Hiro to link with and severely injured Zero Two. She kisses Hiro to link with him, much to Zero Two’s dismay and she attempts to save him before the princess takes him and Strelizia. She then loses consciousness after realizing Hiro delayed the self-destruction of Hringhorni.
After waking up, she decides to rescue him and finds him close to death, so she kisses him to revive him. They reconnect and fight back against VIRM, who retreat.
Following the battle, Hiro finds Zero Two has been left in a catatonic state. Over the next few days, he tends to her but she doesn’t respond to him and mysterious injuries begin appearing on her body, and she begins wondering around and stares at the sky. He finds the last page of her picture book is blank and he realizes she did this on purpose because she anticipated they would part ways. He touches her horns with his and discovers she is mentally connected to Strelizia and she is fighting in space. He decides to go to space and rescue her despite the protests of his friends who say it is a suicide mission. In response to Goro’s protest, Hiro says Zero Two kept her end of their promise, so he can’t leave her behind or else he will feel guilty and he is better off dead if Zero Two doesn’t smile at him.
During the galactic battle, Hiro reaches Strelizia and connects with it to enter Zero Two’s consciousness, which is filled with pages from her picture book. She pleads with him to stay from her because she wants him to stay as a human but he says he wants to be with her forever. She says she is a minster and she is fine with being alone but he calls her a liar because that wouldn’t be true if her last page is blank. He asks her to let him stay with her so they can rewrite the story’s ending. He is on one knee with one hand offered out to her and she accepts, and he vows to never let her go, symbolically marrying each other. Strelizia evolves into Strelizia True Apus which is of Zero Two wearing what resembles a wedding dress and the two enter a warp gate with a klaxosaur bomb to end the war with VIRM for good.
Over the next two years of traveling in space, Upon reaching the VIRM home planet, their connection is severed and Hiro’s consciousness begins fading while Zero Two is attacked by VIRM. She begs their friends to save him and they realize something is amiss, send their prayers to them. Zero Two tells Hiro that humans are strong and all their lives turned out like this because of Hiro. He says it’s not something to be proud of because he caused them trouble but she says it was because of his desire to live. She says he is special to her and he is the humanity she has so desperately needed, adding they met by chance, they are bound by a kiss, and are attracted to each other by nature, and asks him to join her. Upon reconnecting, Zero Two says they are the Jian and they kiss. She says she feels Hiro making her stronger and she is blessed to have been born and met everyone, and she loves Hiro, who declares he loves her too. They detonate the bomb and acknowledge they are about to die. However, both are not afraid and the path they walked on will be taken on by the others. Zero Two believes they will meet on Earth and pick up where they left off as long as their souls exist, and they profess their love to each other one last time before the bomb explodes, destroying the planet and killing Hiro and Zero Two. Holding hands, their souls begin making the long trip back to Earth.
A thousand years later, their souls return to Earth and reincarnate into two children who meet at a cherry blossom tree. The boy is reading Zero Two’s picture book when the girl accidentally trips next to him. After asking if she’s okay and offering his hand out to help her up, she asks who he is. He introduces himself and a new story begins, suggesting they will rekindle their romance.
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The initial interactions of Hiro and Zero Two in the manga almost mirror those in the anime until the squad’s first sortie. When the mission is sent on their first sortie, Zero Two secretly takes Hiro to get a glimpse of the city like she did in the anime but in co ready to the anime, they are found by Nana and taken to the briefing room where they see the mission goes disarray when more Klaxosaurs appear. As Hiro is not permitted to pilot with Zero Two, Mitsuru volunteers to go with her despite Zero Two’s refusal. Hiro almost agrees to this suggestion but changes his mind and insists he will be alright because he has yet to suffer any effects from piloting with her. Nana ultimately gives them permission to pilot to rescue the squad and Hiro, thrilled and overcome by the power he feels, almost succumbs to his cockiness before Zero Two calms him down and they kill the Klaxosaurs. Hiro feels that he has found a new reason to fly, which is Zero Two.
The progression of their relationship is almost identical to the anime events, but the fallout of their relationship is slightly different. When Zero Two starts to become obsessed with her goal to become human and why she has yet to become more human after being with Hiro for a while, her horns grow and she becomes increasing hostile. Hiro notices this change in her and his attempts to get her to open up to him backfire as she rejects his concern. She further calls him her fodder and he has nothing to do with her. He is outraged and says he vowed to be her partner forever, elaborating he has everything to do with her and he will protect her.
When Zero Two was manipulated by the Klaxosaur Princess into attacking Mistilteinn, Hiro forced his way into Strelizia to try and save her. Upon trying to connect with her, she began strangling him and revealed her goal to become human was so she could find her long lost darling. Their minds connected too deep, causing them to remember their erased memories of their childhood together.
Upon realizing Hiro is her long lost darling, Zero Two was overcome with guilt for deceiving and hurting Hiro, so much so that she decided to leave Squad 13 and return to fighting alone. After being unconscious for ten days, Hiro woke up in the hospital and learned of Zero Two’s departure, which saddened him. However, Squad 13 announced they would help Hiro reach Zero Two while she was fighting alone at the Gran Crevasse.
Upon reaching the frontlines and finding a damaged Strelizia, Hiro rushes towards the FRANXX and finds Zero Two unconscious. She tells herself that she is willing to do anything to protect the world Hiro lives in and will sacrifice herself if it means Hiro will live. When she wakes up and finds him holding her, he is overjoyed that they are together again. She pushes him away, as she thinks he should fear or hate her for using him and he has horns like her. Hiro shouts that doesn’t matter because, after reading the story of her picture book and remembering it’s sad ending of the prince and beast princess being separated, he is determined to stay with her forever so they can rewrite the ending of that story. This deeply touches Zero Two, who sheds tears of joy.
When they reconnect, Strelizia evolves and its power increases as a result of their radiance of life. This makes 001 jealous of them, in addition to their mutual, powerful desire to protect their will to live. As they destroy 001, Hiro and Zero Two recall the story of the Jian. After the battle ends, Zero Two wonders what will happen to them and Hiro assures her that they will be alright in a new, unknown world as long as their friends will be with them. Zero Two asks Hiro if he will stay with her forever and he swears they will. Zero Two tells Hiro that she loves him and they kiss.
In an illustration of the final volume, HiroZero are shown holding hands as the squad is together and Zero Two is wearing the standard parasite uniform to symbolize that she genuinely considers herself part of the squad.
In the first Drama CD, when Hiro eats mushrooms that cause the water to fall asleep and have strange dreams, he had an amusing dream about Zero Two that causes him to laugh profusely. When he wakes up, Zero Two becomes intrigued and tries to get Hiro to eat more mushrooms with her but he refuses and wants to throw them away. However, she secretly gives him one and then takes one herself because, as she tells him after they wake up, she wanted to share a dream with him. Hiro wakes up in his bed and is embarrassed to see Zero Two laying with him. He then tells her that he dreamed of them riding a bicycle together through a row of cherry blossom trees.
In the second Drama CD, the squad is in distress as they suspect a strange creature is in the house and Zero Two heightens their anxiety with stories of a monster, which also makes Hiro nervous. When Hiro is captured and knocked unconscious by the creature, Zero Two is worried for Hiro but her concern immediately turns I to rage and she sets out to confront the creature, resulting in further chaos.
In the third Drama CD, two years had passed since leaving Earth. Hiro realizes he is becoming a klaxosaur but tells Zero Two he is not scared because he feels that he is becoming part of her. She also worries that he is getting weak after he rarely falls asleep. To pass time, they role play as a married couple, such as Zero Two playing the doting wife preparing a delicious meal and warm bath for Hiro after he pretends coming home from work and calls her ‘honey’. However, Zero Two says this is unfulfilling and they can’t get married like this. Hiro asks her if she still wants to get married, and attempts to recite the wedding vows. She says they don’t need the vows because they already promised to be together forever. Hiro comments how they spend their time discussing trivial topics he read from books and he mentions how he doesn’t have the need to eat and sleep due to his body turning into one of a klaxosaur. A VIRM fleet attacks them but they quickly eliminate it. Zero Two says she feels stronger with him.
As Kokoro is giving birth to her and Mitsuru’s daughter, Ai, Hiro realizes the baby is about to be born. Zero Two assures him that Kokoro and the baby will be alright, and Hiro wonders what Mitsuru will name the baby. He feels pain in his head and Zero Two says it’s because of the battle damage and metallic waves in space. She asks him to get some rest but he reminds her that he doesn’t need to sleep. Nevertheless, he falls asleep and she says that she is happy but her only regret is that he will never have his original human body again.
Two years since leaving Earth, Hiro wakes up from sleeping and she notices how weak he is has gotten, and asks him not to push himself. He tells her that he had a dream in which all their friends were living good lives on Earth. He also says he had another dream in which he and Zero Two meet in a distant future and he believes this represents hope for them.
It is the most popular ship of the fandom due to it being the central point of the show's plot. It made it to the list of top 10 anime ships, being in the top 10 since the series debut. HiroZero reached 6th place, behind MitsuKoko, after they confessed their love to each other. Following their sacrifice during the finale, they rose to 4th place.
While HiroZero wasn't an official ship until Episode 15, many of the show's fans shipped them. Some even predicted a previous meeting during their childhood which made them "instantly attracted" to each other, which was confirmed in Episode 13.
Some DARLING fans dislike this ship as they feel their relationship was toxic. Some called out Zero Two for manipulating and using Hiro for the first half of the show. However, other fans will point to their interactions in the second half of the show as proof that their relationship is healthy. Some argue that the blame for the toxicity in the first half should also lie with Papa, who tore the two apart as children and tried to wipe their memories, additionally manipulating Zero Two to believe killing klaxosaurs would turn her human.
HiroZero was nominated for Couple Ship of the Year at the Anime Trending Awards 2019, and was placed 4th out of 20 nominees.
- “Let me get a taste of you. After all... you are now my darling!”
- — Zero Two to Hiro before kissing him for the first time.
- “I’m your partner. I’m not going to leave you alone”
- — Hiro to Zero Two.
- “Once we get out of here... I want to be with you forever too. And then I'll be your Da.”
- — Hiro to Zero Two when they were children.
- “The picture book... You were the girl with the picture book back then, weren't you”
- — Hiro to Zero Two after remembering his past.
- “You're my wings, right? If I'm with you, I can fly anywhere I want... We'll always be together right.”
- — Zero Two to Hiro.
- “Zero Two, I love you! I love you for who you are!”
- — Hiro to Zero Two when he confessed.
- “Darling, I love you!”
- — Zero Two to Hiro after reconciling.
- “I hereby vow to never let you go.”
- — Hiro to Zero Two.
- hiro x zero two tag on Tumblr
- zero two x hiro tag on Tumblr
- hiro x 002 tag on Tumblr
- 002 x hiro tag on Tumblr
- hir02 tag on Tumblr
- DARLING's director, Atsushi Nishigori, said he always intended for Hiro and Zero Two to have a happy ending but felt he needed to make their fate more sentimental after discussing it with his assistants. So he went ahead with them making the decision to give up their own lives to save those of their friends and start over as humans via reincarnation.
- Hiro’s first kiss was with Zero Two, but it is unknown if Hiro was Zero Two's first kiss.
- By his own admission, Zero Two is the first girl Hiro as seen naked, although by accident.
- It was Hiro reading The Beast and the Prince to her that Zero Two learned the word darling.
- According to Zero Two, even before she realized he was her long-lost darling, she couldn’t bear to watch Hiro suffering and would go out of her way to help even people she didn’t get along with (such as Ichigo) if it would make Hiro smile.
- In the third Drama CD, Hiro expresses he still wants to get married, but Zero Two tells him there is no point in that because they already promised to be together forever. From their perspective, marriage simply means a vow to be true to each other in sickness and health until parted by death.
- Zero Two asked Hiro to draw a picture of the prince to add as a page in her picture book but he was too embarrassed to show her. Despite being amused at how terrible his drawing skills were, Zero Two decided to include it in her book with the notation ‘My Beloved Darling’.
- As they are the main coupling, Hiro and Zero Two were the first ones to kiss. However, they are never shown to consummate their relationship.
- Hiro’s English voice actor, Matt Shipman is ironically married to Ichigo’s English voice actress, Brittany Lauda, in real life.
- Hiro’s code number is 016 and Zero Two’s code number is 002. When subtracted, is the number 14, the number of the episode in which they are separated and have a falling out. When added, it is 18, which is the number of the episode in which they reaffirm their promise to get married. When divided, it is 8, the number of the episode in which Zero Two initiates the bathroom fight to be more human and Hiro feels the desire to take care of her.
|SHIPS||het||Delpha • FutoKoko • FutoKuno • HaNa • HiroIchi • HiroMi • HiroZero • IchiGoro • MitsuKoko • MitsuKuno • ZeroMitsu • ZoroMiku|
|femslash||IchiKuno • IkuNao|