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