In a battle against the klaxosaurs only the children, classified as parasites, are humanity's hope in this dying world. Fighting in mechanized suits known as FRANXX, parasites are grouped up in male and female pairs to face the monstrous creatures. Hiro was once a prodigy FRANXX pilot. But when he gives up the fight, he meets Zero Two, the girl with the horns, and finds a new reason to keep going.

Gear finds out that General Alex is his father, but cannot rescue him because of the wound Alex got in the cell. Tejirov tells Gear that he must instead absorb Alex. He refuses at first, but Alex said says he has no choice and forces Gear to touch him. Before he is absorbed, he tells Gear the story of his mother, the only killer Alex considered to be his equal, whom he had to absorb after they were so badly wounded in combat that they could only survive...