Zero Two

Since childhood, Zero Two had been alone due to her Klaxosaur blood, always being seen as a "monster". The way people treated her as a child made her lose faith in people which is especially seen when she was a child: being very defensive or aggressive when people tried to interact with her. Besides that, Zero Two acted like a wild animal or a feral child, eating with her hands, growling, making other vocal noises instead of speaking and chasing after mice that were near her. However, Zero Two was also shown to a fairly cheerful, curious, and happy girl, and it was during her time with Hiro that shaped much of her personality and quirks in the present, such as her sweet tooth, the way she referred to herself as ("Boku"), and the nickname she had for Hiro, "Darling". Because Hiro treated her as he would anyone else, whereas others didn't treat her as a human for one reason or another, Zero Two developed a deep admiration and liking towards him. Despite having her memories of the darling from her childhood erased, Zero Two retained some fragmented memories which was why she strived to become human no matter what.

As she grew up, Zero Two's personality was rumored to be dangerous, cold, and alluring. She was an elite pilot with the pseudonym "Partner Killer", given the mysterious cases of her co-pilots dying after only three sorties FRANXX rides. However, she appeared to be playful towards Hiro and sometimes showed humor; which is evident during their first meeting, in which she teased him and called him a "pervert". However, she prioritized her duty as a Parasite more than anything, not because she wanted to protect Papa and the others, but because she wanted to "become human". Her outlook on life was quite cynical which is why she didn't bother with a name since they were all meant to fight and die. She had also been a prized military asset of APE and sent to fight on the front lines for so long that she had no regard for human life or her own since they all would become a statistic when they died anyway. When people around her died, she hardly batted an eye at it because, to her, it was just a fact of life that everyone dies. Zero Two always kept people at arm's length with mocking humor, nihilism, and emotional detachment. Zero Two also freely talked about how much she hated their society. However, after seeing Hiro's determination to pilot with her, Zero Two noted that they were very similar and she invited him to partner up with her, despite having fought alone during the majority of her life and never leaning on others for support.