After alien technology falls to Earth and humankind uses it to develop giant robots with applications in industry and security, Japan and other countries create academies to train students to use them. An aspiring robot pilot, Maki Natsuhito, tries his best but his prospects in the field look dismal, not helped by the fact that his crush, Asato Kana, is one of the school's aces.

Everything changes with the arrival of Fishes, a mysterious smiling girl who offers Maki the power to fight a new alien threat, but who exacts a heavy price on the exchange. Now in possession of abilities others could only dream of, Maki will find that the idea of a hero is very different from practice.