Upon their recapture, both children have their memories erased by the adults, explaining why they didn't initially recognize each other at the start of the series. Themes and Symbolism
Hiro discovers a young, red-skinned, and horned Zero Two being subjected to brutal, torturous experiments by Dr. FRANXX to test her regeneration. Darling in the FranXX Episode 13
The revelation recontextualizes the Strelitzia 's true power, which is unlocked only when the two pilots share a genuine, deep-seated emotional bond. Upon their recapture, both children have their memories
Both Hiro and Zero Two are portrayed as isolated figures—Hiro by his curiosity and Zero Two by her physical imprisonment—who find meaning only in their mutual rebellion. During their brief time in the snowy wilderness,
Moved by her suffering, Hiro breaks her out of her cell. During their brief time in the snowy wilderness, they share a picture book—also titled The Beast and the Prince —which becomes the foundation for Zero Two’s desire to become "human" and find her "Darling" again.
The Beast and the Prince: A Deep Dive into Darling in the FranXX Episode 13