In a post-apocalyptic future, humanity is under constant threat from giant creatures known as klaxosaurs. Pushed to the brink of annihilation, humanity abandon Earth's now desolate surface for mobile fortress-cities known as Plantations. To defend the Plantations, children called parasites are raised to pilot giant mecha known as Franxx 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 elite Franxx pilot with klaxosaur blood, and an infamous reputation as the "Partner Killer". The rumor is that Zero Two's partners will die after riding with her for the third time. Despite this, after Zero Two's partner is killed during a klaxosaur attack during the graduation ceremony, Hiro volunteers to become her new partner, or as Zero Two calls him, "Darling".