Short Answer: After ingesting the blood of Zero Two, Hiro’s body began to experience genetic changes as the number of yellow blood cells in his body increased rapidly and it was because of these changes that he lost the ability to pilot a Franxx with the pistils around him.
It is important to note that Hiro didn’t lose his piloting abilities. Instead, he became so overwhelming that pistils couldn’t maintain a connection with him. Since Klaxosaur blood streams through his veins, Hiro can only pilot with Zero Two, who also possesses Klaxosaur blood.
Let’s take a look at the events surrounding Hiro in order to truly comprehend why he is unable to pilot a Franxx with other pistils.
Hiro when he was a child
Darling in the Franxx features emotionless children as Dr. Franxx artificially created them for the sole purpose of piloting Franxx, but Hiro was an exception as he had emotions and even dreamed of leaving this place called Garden to explore the outside world. Hiro was different from other children in various aspects; like he had a cheerful personality like ordinary children, which compelled him to show kindness to other children. He is the one who first introduced the concept of naming children with respect to their given codename, and this act influenced other children to the point they began to show some characteristics of normal human children.
Although adults treated Hiro as a significant child because of his high aptitude for Franxx, he still wanted to leave Garden as the outside world continued to intrigue him. Moreover, Hiro had a habit of questioning the actions of adults, unlike other children who obediently followed the rules like programmed robots. Through a series of events, Hiro witnessed a girl covered in red skin with horns getting tortured by adults. He ended up getting fascinated with her to the point he mustered his courage and helped her escape the facility.
Although the girl first showed him her repulsive side, she eventually became attached to him as Hiro named her Zero Two as she had the codename 002. However, soon adults cornered them and punished them by removing their memories, causing Hiro to develop a serious and obedient personality, as shown in episode 13 of Darling in the Franxx.
What is needed to pilot a Franxx?
Dr. Franxx created bio-mechanical weapons called Franxx to counter the attacks of Klaxosaurs as all other weapons at humanity’s disposal failed to affect Klaxosaurs. As far as Franxx go, they basically follow the same operating mechanism as Klaxosaurs and Dr. Franxx himself acknowledged that he just copied the mechanism of Klaxosaurs and implemented it into mechas called Franxx, as shown in episode 19 of Darling in the Franxx.
Since Franxx are exact copies of Klaxosaurs, they require a pair of fertile male and female to pilot it as Klaxosaurs also came into being when male and female Klaxo Sapiens merged their bodies with mechas. However, not just fertility is required to pilot Franxx; all children must be given Yellow Blood Cells extracted from Magma Energy in order to pilot Franxx. It is important to note that the piloting pair must be compatible with each other to create a successful synchronization like Ichigo couldn’t maintain linking with Hiro because the two weren’t compatible with each other, as shown in episode 2 of Darling in the Franxx.
Moreover, the children are carefully paired with each other after thorough checking and test trials to avoid any chaos, as an unsuccessful linking and pairing results in severe damage to the male or even female like Mitsuru rode with Zero Two and ended up getting heavily damaged as shown in episode 3 of Darling in the Franxx.
What happened to Hiro when he licked Zero Two’s wound?
Hiro rescued Zero Two from the facility, and together they decided to flee from this caged life. At first, Zero Two considers him hostile like other humans and bites his hand, but despite the pain, Hiro pats her head, causing Zero Two to develop trust in him. As they make their escape, Zero Two gets injured and blue blood sprouts out of the wound, surprising Hiro as he had never seen a being with blue blood. Hiro ends up licking her wound to heal it because he read in a book that animals lick their wounds to heal them, as shown in episode 13 of Darling in the Franxx. This specific act of licking caused Hiro to ingest Zero Two’s blood which caused him to lose his piloting ability because the blue blood belonged to the Klaxo Sapien Race while he was a human. Gradually, the Klaxo Sapien blood altered his genetics to the point he couldn’t pilot Franxx with any of the pistils, causing him much grief.
Later, Hiro gained a glimmer of hope as he managed to pilot a Franxx with Zero Two, while the other parasites continued to wonder why Hiro could ride with her when countless others died just by piloting Franxx with her. Since Hiro had ingested Zero Two blood in childhood, he developed a high resistance to the overwhelming experience that comes while piloting a Franxx with Zero Two. The continuous bonding of Zero Two and Hiro further increased the impact of ingested blood on Hiro’s body and ultimately, he became a Hybrid Klaxo Sapien like Zero Two, as shown in episode 24 of Darling in the Franxx.
Why can Hiro pilot a Franxx with Zero Two?
Zero Two was known as Partner Killer because every stamen that rode with her died sooner or later. However, Hiro managed to pilot with Zero Two more than three times, but he also developed a blue tumor on his chest, as shown in episode 5 of Darling in the Franxx. Despite knowing the consequences, Hiro decided to pilot with her again and ended up suffering in the middle of the fight, but he refused to give up and reversed the tumor effects with his willpower, as shown in episode 6 of Darling in the Franxx.
Here’s a short clip from Darling in the Franxx where we can the blue tumor on Hiro’s chest.
Later, Hiro and Zero Two developed a romantic bond that even increased their compatibility with each other. It is important to note that Zero Two had Klaxosaur Blood that caused other stamens to die from exhaustion, but Hiro had already ingested her blood in the past, and after several rides, the blood altered his genetics to match Zero Two’s, creating strong piloting compatibility between them. It wouldn’t be wrong to conclude that the piloting pair must belong to the same race in order to maintain a strong connection with each other while piloting Franxx.
Moreover, Hiro and Zero Two bear strong romantic feelings for each other, and after remembering their past encounter, they unlock more power and even greater compatibility in piloting Franxx, as shown in episode 15 of Darling in the Franxx. Given all this, it is safe to say that Zero Two and Hiro’s love for each enabled them to emerge as the most powerful Franxx pilots of all time.
You Might Also Like: Why is Ichigo so Hated?
Darling in the Franxx features lovable characters, but among them, a character named Ichigo is hated by fans because she comes off as an arrogant girl who promotes hate about the female protagonist named Zero Two. She also tries to push herself on Hiro, which prompts the fans to criticize her. However, that’s not the end of it, as there are reasons behind Ichigo’s actions that lead her to become a subject of hate.
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