Takuya Arima, a youthful academic, is struggling to come to terms with his father's sudden disappearance. His renowned historian father, who had undertaken extensive research, vanished mysteriously. During one summer vacation, Takuya is sent an uncommon package from his absent father, which includes a letter revealing the existence of various parallel universes. At first, Takuya disregards the notion, but as he finds a tool that can transport him to different realms, he wonders if his father is still alive and where he could possibly be.