Living with the Touma family after losing his parents, Yagi Takeru is under the care of Touma Rokunosuke. His circle includes the competitive yet friendly Yamato Takeshi from the kendo club, the Shiratori sisters Kotono and Asuka, and his childhood companion Oosu Seri. A seismic event shatters their tranquil existence as the school transforms into an ancient, desolate wasteland devoid of its inhabitants. With the sudden disappearance of teachers and classmates, Takeru teams up with Seri and Asuka to escape the eerie remains, only to discover their hometown deserted. Encountering mysterious cloaked figures, they learn of their involuntary transport to a foreign realm, forever altering their reality.