In a distant future, humanity teeters on the brink of extinction because of colossal beasts known as Klaxosaurs. The survivors reside within massive, fortified metropolises called Plantations. Within these walls, children are raised exclusively to operate giant mechas termed FranXX, which combat the Klaxosaurs in mandatory male-female pairings. Bred solely for this purpose, these pilots grow up isolated from the outside world, convinced that their sole function is to defend humanity.
Hiro, a prospective FranXX pilot, is left demoralized and lacking self-assurance after failing an aptitude test. He skips his squad's graduation ceremony and retreats to a secluded forest lake, where he encounters a mysterious girl with two horns protruding from her head. She reveals her codename is Zero Two, a legendary pilot infamous as the "Partner Killer." As Hiro attempts to make sense of this encounter, a Klaxosaur assaults the plantation. Zero Two engages the beast with her FranXX but sustains severe damage, crashing her mecha near Hiro. Discovering her original partner is dead, she requests that Hiro join her as a pilot. Together, they effortlessly vanquish the Klaxosaur. With Zero Two at his side, Hiro gains a second opportunity to surmount his previous failures, though the price remains uncertain.
