In the distant future, a polluted world has been overrun by havoc-wreaking creatures called contaminoids. Humanity, having been forced to relocate, must live in isolated mobile cities called Regios. Layfon Alseif, a young man with a mysterious past enrols in the Academy City of Zuellni intending to be a regular student in the Liberal Arts track. Nina Antalk, the leader of the 17th Military Arts Unit is troubled because a member of her unit has just quit, so they are short-handed and due to be disbanded. They need to find a replacement soon.
Just before the general assembly on the first day of classes there is a destructive altercation between two Military Arts students who use their Kei powers, and a girl is caught in the crossfire. Layfon intervenes, showing extraordinary skill in saving the girl, and he immediately catches the eye of Nina and the president Karian Loss. The president drags him into his office and forcibly makes him transfer to the Military Arts track, despite his objections, and when Nina arrives, he is reluctantly assigned to her unit.