Humanity has fled from Earth and taken up residence in the "Tenjo" upper world, leaving behind a ruined planet. But when Tenjo collapses due to war and causation, they are forced to return to Earth, which is now uninhabitable, save for Shinshu. As Shinshu is small, the humans replicate the area, creating "Juso Sekai". Despite the obstacles, they begin to recreate history, going all the way back to B.C. 10,000 in order to rebuild Tenjo and restore causation. After reproducing history up until A.D. 1413, war breaks out in Shinshu, causing Juso Sekai to revert back to the original world. The humans in Juso Sekai are now landless and invade the original world, leading to Shinshu's defeat and division by the invaders. Although history reproduction resumes in A.D. 1457, it comes to a stop in A.D. 1648, leading to rumors of a looming apocalypse spreading throughout the world.
