The story takes place in an unspecified future date, referred to as the 71st year of the True Era. 70% of all human beings have migrated from Earth to other planets of the Solar System and a Dyson sphere, constructed around the Sun. The world is divided between two superpowers called the Dorssia Military Pact Federation and the Atlantic Ring United States(ARUS), and a small neutral nation called JIOR that has prospered economically. In the same year, the Dyson sphere, built by JIOR, is invaded by Dorssian military forces.
Haruto Tokishima, a student from Sakimori High School living on the sphere's "Module 77", discovers a mysterious and powerful mecha called Valvrave and uses it to defend the module from a Dorssian invasion that takes over the rest of JIOR. Once they learn that both Dorssia and the ARUS intend to claim the Valvrave for themselves, with no concern with their lives, the students of Sakimori High declare Module 77 an independent state and abandon JIOR territory. Soon after, several other Valvraves are found inside the school and some of them are claimed by other students who join Haruto's fight to protect it. Once Haruto is approached by L-elf Karlstein, a Dorssian spy who claims to have the intentions to one day stage a revolution in his own country, both join forces in an unlikely alliance to secure the sovereignty of their newfounded nation.