Satoyasu

From Baka-Tsuki: The world was once at war with 10 alternate worlds. This was known as the Concept War and our world won 60 years ago. All of this was concealed so no normal people are aware of this fact in the current time. After the death of his grandfather, the high-school student Sayama Mikoto is suddenly summoned by the giant corporation IAI. He learns this world is…

In the far future, humans abandon the devastated Earth and move to the upper world "Tenjo". But Tenjo and the law of causation collapse from a war and humans return to the Earth, which has turned into an uninhabitable planet, with the exception of the Divine State area. The Divine State is too small to accommodate all the humans, so they duplicate the area and create the "…