Kyoukai Senjou no Horizon境界線上のホライゾン; 境界线上的地平线; Horizon in the Middle of Nowhere; Horizon on the Middle of Nowhere; Kyōkai Senjō no Horizon; Kyoukaisenjo no Horaizon

In the far future, humans abandon the devastated Earth and move to the upper world "Tenjo". But Tenjo and the law of causation collapse by a war and humans returns to the Earth, which has turns into an inhabitable planet except for Shinshu area. Shinshu is too small to accommodate all the humans, so they duplicate the area and create "Juso Sekai". In order to rebuild Tenjo and the law of causation, the returned humans start reproduction of history from B.C. 10,000. When the reproduction completes until 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 is divided by the invaders from Juso Sekai. They try to resume the history reproduction from A.D.1457, but the update of history terminates in A.D.1648. A rumor of apocalypse begins to spread around the world. - Wikipedia