High school student Eiji is in love with Aki, the head of the tennis team, but he is unable to ask her out. Another student, Yuki, discovers his obsession with Aki, and promises to help him get closer to her...

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 uni...