Hiro and Mitsuru have known each other since they were small children living in the Garden. When Hiro began naming all the children, Mitsuru shyly asked if Hiro could give him a name, which Hiro did. Following this, Mitsuru idolized Hiro and often followed him around, admiring him for being a genius.
When they were 9-years-old, Mitsuru decided to risk his life and get an Elixir Injection to increase his aptitude results. However, before going to get the injection, he told Hiro that he wanted to become a parasite and fight alongside him, and if he came back alive, he wanted to pilot a FRANXX with Hiro. Hiro agreed and they pinky promised. Following the procedure, Mitsuru survived and went to see Hiro, who, unbeknownst to Mitsuru, had his memories altered due to running away with Zero Two. Hiro has no recollection of the promise, devastating Mitsuru and shattering his faith in others. Since then, Mitsuru has been determined to surpass Hiro in everything, especially piloting a FRANXX.
When they were 14, they were assigned to the same FRANXX squad. While Mitsuru passed his capacity test with Ikuno, Hiro failed with Naomi and is obligated to return to the Garden but, because of his status as a special specimen, he is offered to stay. Mitsuru doesn’t care what Hiro chooses to do but instead sarcastically asks everyone to consider Hiro’s feelings on failing. This is attitude is likely due to Mitsuru believing he has surpassed Hiro by becoming a parasite whereas Hiro, a child genius, failed to do so.
Following the incident in which Hiro, while unconscious, piloted Strelizia with Zero Two to neutralize a klaxosaur during the startup ritual, Mitsuru didn’t believe it and said Zero Two is capable of piloting a FRANXX on her own. This provoked Zorome to start a physical altercation with Hiro, and Mitsuru simply stood by and watched it. Before the squad’s first sortie, Ichigo’s unwavering trust in Hiro seemingly began to irritate Mitsuru, who said it is best to accept Hiro will never become a parasite and goes in to say that Hiro, who was expected to become their leader and was always special even among the double digits, failed because fate had other plans. He adds they need to cut their losses because he doesn’t want to see this pitiful side of Hiro again.
During the squad’s first mission, Mitsuru offers to pilot with Zero Two to save everyone from being killed by a horde of klaxosaurs after Hiro is refused to pilot with her. Zero Two refuses but Hiro reluctantly tells her to go with Mitsuru. While leaving, Mitsuru tells Hiro he just really wants to prove he is a better pilot than him. Hiro feels uncomfortable seeing Zero Two go with Mitsuru, as he really wanted to pilot with her. During the battle, Mitsuru becomes empowered by the experience and parades how he can be a better partner to Zero Two than Hiro, which troubles Hiro. At the end, Hiro notices that Mitsuru doesn’t come out of the cockpit, as he is severally injured and traumatized. While recovering, he warns Hiro not to pilot wth her again or else she will kill him. This makes Hiro feel torn on what to do.
After Hiro rides a second time with Zero Two with no issue, Mitsuru reacts with jealousy as everyone praises him and he goes to the greenhouse to sulk, where he is found by Kokoro. During Hiro’s third ride, he almost succumbs to the effects and Mitsuru reacts with horror that Hiro may be dead. However, Hiro miraculously survives. Upon seeing Hiro emerge with Zero Two from the cockpit, Mitsuru and the others go to congratulate him, though Mitsuru doesn’t speak to him.
While on a vacation to the beach, Mitsuru tells Ikuno how Hiro is smiling now whereas he was acting depressed and suicidal recently. Later that night, after exploring an abandoned modern city, Hiro wonders why humanity abandoned the surface for the plantations. Mitsuru defends Papa, saying it was to protect humanity from the klaxosaurs.
Shortly after, Mitsuru has a dream from his childhood, telling his child self not to look at Hiro with admiration before waking up and reminding himself why he stopping trusting others. Upon falling ill and being hospitalized, Mitsuru continues having a dream of his child self following Hiro around and about the promise. Due to his incompatibility with Ikuno, Nana proposes the squad try a partner shuffle. Ikuno deduces Mitsuru really wants to be acknowledged not just by Papa and the others but by Hiro, and he tells her to be quiet, which causes everyone to stare at him. Seeing Hiro, Mitsuru feels angry and ashamed for making a scene. After being paired with Kokoro, which devastates Futoshi, Mitsuru is indifferent to the arrangement and this angers Futoshi to the point he tries to attack Mitsuru but misses. As Mitsuru walks away, Hiro stops him and asks him to understand but Mitsuru angrily retorts Hiro is in no position to tell him that.
Later that day, while in a battle, Mitsuru shuts Genista down out of despair for not killing the klaxosaur and Kokoro gets him to confess that Hiro breaking their promise is what made him unable to trust others. Mitsuru starts breaking down and cries, saying that Hiro should have never made the promise if he didn’t intend to keep it. Kokoro says it must have really hurt him but she says she also hurt someone (Futoshi) by breaking a promise and she understands if Futoshi is angry at her. Mitsuru asks if she means he should forgive Hiro but she says that is a choice only he will have to make. After he and Kokoro reconcile and return to the fight, Mitsuru tells himself that he doesn’t know if he can forgive Hiro but he is willing to be more civil for the sake of carrying out the squad’s duties.
During a trip to the Garden to undergo testing, Hiro is surprised to learn Mitsuru went to the lab once before, which irritates Mitsuru. A couple of days later, after Hiro is hospitalized when Zero Two tried to kill him in a moment of rage, Mitsuru is in his room with the others. As they all start to leave, Hiro calls out to Mitsuru and brings up the promise, now that he has regained his memories. Mitsuru is surprised but then says he forgot about it a long time ago, implying Mitsuru is aware why Hiro forgot about it and he is willing to let it go. Mitsuru tells Hiro not to go near Zero Two again before leaving. However, as Ichigo tries to ban Zero Two from seeing Hiro, Mitsuru and the others grow tired of it and convince Ichigo to let the two meet anyway, which goes horribly wrong.
For the siege of Gran Crevasse, Hiro is grounded while the others go into battle. His friends vow to protect him. Hiro thanks them and all of them, including Mitsuru, smile.
A month later, Mitsuru and Hiro inspect the water in a lake, which they notice is foul and start to wonder ways to filter the water. Mitsuru later talks to Kokoro, who gives him a haircut, about how his grudge against Hiro was uncalled for since Hiro did nothing wrong and he wonders why he was expecting from Hiro if the latter lost his memories. He now believes he used the grudge to give himself a drive and, without it, he has nothing. Kokoro praises him for being able to resolve the misunderstanding and start over to rebuild his friendship with Hiro. When Hiro and Zero Two suggests they all cook their own dinner, Mitsuru quickly agrees but doesn’t say it out right to Hiro, who looks at him in appreciation.
As Mitsuru struggles with his growing feelings for Kokoro and her sudden advances towards him, Hiro finds him standing by the lake and they lay in the water together. Mitsuru says he doesn’t understand and Hiro notes how much he’s changed, due to that Mitsuru has never been so close to another person. Hiro says Mitsuru wants to get to know Kokoro more and, because Hiro loves Zero Two for that reason, he says that’s what it means to love someone. Mitsuru takes all this in and realizes he is in love with Kokoro. Hiro thinks he confused Mitsuru but he says it’s fine and he is glad they got to talk like this in a long time.
Hiro later tells Mitsuru and Kokoro the meaning of marriage, and they decide to get married themselves before the squad leaves for the Bird Nest. However, on the day of the wedding, the 9’s and an APE assault team crashes the wedding and takes the two away. This angers Hiro, who realizes parasites are not even entitled to their own happiness and he worries about those two. A couple of weeks later, it is revealed their memories of each other have been altered as punishment. Hiro becomes consumed with anger towards Papa for doing this and it provokes him to confront Papa, who justifies the memory wipe on the grounds their actions would have jeopardize APE’s objectives. Hiro says him and the squad no longer see him as their papa and he demands they be set free. Papa agrees in exchange for their cooperation in the supposed final battle against the Klaxosaurs, which Hiro accepts.
A few days later, Hiro and the others are shocked when it is revealed Kokoro is pregnant with Mitsuru’s child. While Mitsuru is confused and scared on what to do regarding the options of abortion or keeping the baby, he asks Hiro for advice. However, Hiro, lost in concern for a catatonic Zero Two, doesn’t even know what is right and wrong anymore, and can’t give him an answer. The next day, Hiro announces he is going to space to rescue Zero Two despite it being a suicide mission. Mitsuru doesn’t say anything but appears troubled as Hiro explains his reasons, including that he is better off dead if Zero Two can’t smile for him. These words have a big impact on Mitsuru as he contemplates on what to do regarding Kokoro’s pregnancy. Seeing how Hiro is risking everything to protect what means the world to him (Zero Two), Mitsuru realizes his unborn child is the most important thing in the world to him and he makes the decision to forgo participating in the battle against VIRM to reconcile with Kokoro and prove to her that he wants her to keep their baby.
Before Hiro and the squad leave for space, Mitsuru tells Hiro his decision to stay behind with Kokoro. Hiro replies he understands and that Mitsuru wants to reconcile with Kokoro, which Mitsuru confirms. Eight months into HiroZero’s space traveling, Hiro realizes the baby will be born soon and he wonders what Mitsuru will name his child.
Two years later, while Mitsuru and Kokoro’s daughter, Ai, plays near Zero Two’s statue, she begins saying “darling”. They realize something is wrong with Hiro and Zero Two, and everyone joins hands to send their prayers to the two in space. Mitsuru says he chose the name ‘Ai’ for his daughter because it means ‘love’, a word he and Kokoro were never taught but learned from Hiro and Zero Two. Mitsuru adds that he and Kokoro want her to inherit the bond Hiro and Zero Two have. Hiro, having been knocked unconscious by a sudden attack by VIRM, regains consciousnesses upon hearing about Ai. When Hiro and Zero Two sacrifice themselves to destroy the VIRM home planet, Mitsuru mourns the loss of his two friends
Eight years later, Mitsuru and the rest of the squad reunite at a cherry blossom tree to remember Hiro and Zero Two, and all the lessons they learned from those two.
The shipping was initially descent among the fans due to Mitsuru’s obsession with his broken promise with Hiro and his childhood admiration of him pointing to evidence of him having a former crush on Hiro. Some fans even theorized that Mitsuru's low paracapacity was because he was only interested in Hiro and not girls (such as his inability to maintain a stable synchronization with Ikuno but he was able to hold a much stronger one with Kokoro). The ship started sinking in Episode 15 when Hiro and Zero Two officially confessed their love for each other. It completely diminished following Episode 17, when Mitsuru acknowledged his feelings for Kokoro and consummated their relationship.
- Hiro’s English voice actor, Matt Shipman, is a HiroIchi shipper because he is married to Ichigo’s English voice actress, Brittany Lauda, in real life. Whereas Mitsuru’s English voice actor, Bryson Baugus, is a MitsuKoko shipper.
- It is because of Hiro’s influence that Mitsuru would find a purpose in life; initially using the broken promise as a grudge against him which made Mitsuru cold towards others. However, this compelled Kokoro to get close to him and help him with this, causing Mitsuru to fall in love with her and leading to the conception of their child. In addition, Hiro is the one to introduce marriage to the two and their memory wipe over this provoked Hiro to rebel against APE.
- During the final battle, when HiroZero were close to losing against VIRM after their connection was cut off, it would be the revelation from Mitsuru that he had a daughter that would help Hiro to regain consciousness and help him reconnect with Zero Two.
- In the manga, Hiro and Mitsuru fulfill their promise to pilot a FRANXX together; as Zero Two was fighting at the Gran Crevasse alone, Mitsuru and Kokoro took Hiro to her location in Genista. Although Hiro didn’t think Mitsuru would let him, Mitsuru says he wanted to make Hiro keep his promise as a way to let Hiro redeem himself.
|SHIPS||het||Delpha • FutoKoko • FutoKuno • HaNa • HiroIchi • HiroMi • HiroZero • IchiGoro • MitsuKoko • MitsuKuno • ZeroMitsu • ZoroMiku|
|femslash||IchiKuno • IkuNao|