Ayato and Yuki are good friends that go to school every morning together, but their relationship has changed in one night. Yuki's purpose is to eat "the human soul" and Ayato's purpose is "to kill Yuki". In order to stop him, the two sides began a bitter battle, and the day after, they pretended as if nothing had happened, it felt it was a dream, so the cycle continues.

(Source: Kawaii-Corner)