Akiyuki Takehara rushes to go to school, stopping by his father's clinic to deliver a lunchbox. Haru Nishimura and Furuichi Teraoka wait for Akiyuki at the school bus before departure. He cleverly allows an unknown Ruikon girl, later recognized as Nazuna, on the bus, not knowing who she is. More and more inquiry airships start to hover over Sentan Island. The peaceful life on this island is disrupted when sudden war breaks out. Nazuna detonates herself in the bus, destroying the school grounds. A glowing substance is emitted from Nazuna before she dies, and it enters into Akiyuki's arm and takes control of his body, as he transforms into a strange creature known as Xam'd.