A small percentage of adolescents have onsets of special abilities. Yu Otosaka deftly uses an ability that takes over a target's body for five seconds to live the school life of an honor student, and gets accepted into a prestigious high school. Just when Yu is about to live a stable life in high school, a girl named Nao Tomori appears before him...

Yu, crestfallen by the fact that he lost his little sister Ayumi, shuts himself alone inside his home and cuts all communication with the outside world. Denying even the worried student council members that came to check on him, Yu leads a dissolute life only to find appearing before him...