Every last Thursday of the month at an all-girls high school, the students of Class 2–5 cast their votes in a popularity poll. The results classify them into Grades A, B, C, D, and F. If they fall into Grade F, they become legitimate victims of school violence.

The story centers on a salaryman who has a reliable wife and a daughter in university who can sometimes act a bit rebellious, but has a happy life in his own way. Until one day he finds out his daughter has been beaten, and thus begins his journey into a dangerous world to protect his family.

A humble office worker's peaceful family life comes to an end after he makes a grave decision for the sake of his family.