Based on a light novel series written by Kawakami Minoru and illustrated by Satoyasu.

In the far future, humans abandon the devastated Earth and move to the upper world Tenjo. But Tenjo and the law of causation collapse in a war and humans return to the Earth, which has turned into an uninhabitable planet except for Shinshu area.

Shinshu is too small to accommodate all the humans, so they duplicate the area and create Juso Sekai in a parallel world. In order to rebuild Tenjo and the law of causation, the returned humans start reproduction of the history from B.C. 10,000. When the reproduction proceeds to A.D. 1413, a war breaks out in Shinshu and Juso Sekai falls onto the original world.

The humans living in Juso Sekai lose their land and invade the original world. People in Shinshu surrender and the land is divided by the invaders from Juso Sekai. They try to resume the history reproduction from A.D.1457, but the update of the history terminates in A.D.1648. A rumor of apocalypse begins to spread the world.