One summer vacation. Five men and women take supplementary classes. In this classroom, there is a student who is not supposed to be there.

During the summer vacation period, temporary teacher Honoka Kimijima is in charge of a supplementary class. One day, a female student suddenly jumps off from the school rooftop and mysteriously dies in front of Honoka. Honoka notices a mystery of a student who is not supposed to be there. Honoka has 5 students in her supplementary class, including Hitomi Miura and Takeru Maekawa. Honoka soon uncovers a shocking truth about that child.