Shidou Itsuka is an average guy who’s not really the most popular guy in school with the girls. However, on a certain day, he meets a pretty “spirit girl”, who is accused to be causing troubles in the world. Thus, many missiles and such are launched at her with the hope to destroy this “spirit”, but can’t harm her at all. Then Tobiichi Origami, a classmate of Shidou, arrives as part of the AST – the Anti-Spirit Team – in order to destroy her, and unlike the missiles and rockets launched at the “spirit”, manages to keep up with that mysterious, nameless black-haired girl. Then, Shidou’s little sister, Kotori, tells him a way to help that girl without destroying her. That is…making her fall in love.