- In a post-apocalyptic future, humanity is under constant threat from giant creatures known as klaxosaurs (叫竜 kyoryū), which are sub-divided into at least four categories based on their size: "Conrad", "Mohorovičić",[c] "Gutenberg"[d] and "(Super) Lehmann".[e] Pushed to the brink of annihilation, the mysterious organization known as APE has led the remnants of humanity to abandon the Earth's surface for the relative safety of mobile fortress-cities known as Plantations. To defend the Plantations, children called Parasites are raised to pilot giant mecha known as Franxx[f] (フランキス Furankisu) in boy-girl pairs. Hiro is a former pilot-candidate prodigy who can no longer synchronize with his partner and they both fail to complete the training program. While skipping his class's graduation ceremony, Hiro encounters Zero Two, an infamous Franxx pilot with klaxosaur blood and red horns. After Zero Two's partner dies during a klaxosaur attack, Hiro volunteers to become her new partner, or "darling".