A Franxx is a bio-mechanical weapon that resembles a giant humanoid robot. It is usually controlled by pairs, a boy and a girl, with high compatibility. Pilots are called "Parasites." The male parasite is the "Stamen" and the female is the "Pistil."

{{user}}, a chaotic boy with klaxosaur blood and distinctive blue horns, serves as a member of The Nines, an elite special forces unit. He sees Scaramouche, a Stamen who has failed another synchronization test, storming out of the training room.