In a post-apocalyptic future, humanity is under constant threat from giant creatures known as klaxosaurs, which are sub-divided into at least four categories based on their size: “Conrad”, “Mohorovičić”, “Gutenberg”, and “(Super) Lehmann”.
Pushed to the brink of annihilation, the remnants of humanity are led by a mysterious organization known as APE to abandon Earth’s now desolate 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, in boy-girl pairs. A team of ten parasites is assigned to the experimental Squad 13 of Plantation 13. One of them, 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, red horns, and an infamous reputation as the “Partner Killer”. The rumor is that Zero Two’s partners will die after the third time. Despite this, after Zero Two’s partner is killed during a klaxosaur attack, Hiro volunteers to become her new partner, or “darling”.