Situated on the outskirts of Tokyo, Hachimitsu Private Academy is a prestigious all-girls boarding school, renowned for its high-quality education and disciplined student body. However, this status quo is set to change due to a revision of the school's most iconic policy, which now allows boys to enroll. At the beginning of the first semester under this new decree, only five boys have been accepted, effectively creating a student ratio of two hundred girls to one boy. Kiyoshi, Gakuto, Shingo, Andre, and Jo are quickly ostracized without having the chance to make any kind of first impression. Unable to communicate with their female classmates, the eager boys set their sights on a far more dangerous task: peeping into the girls' bath! It is only after their plan is thoroughly dismantled by the infamous Underground Student Council that the motley crew finds their freedom abruptly stripped away, as they are thrown into the school's prison with a sentence of an entire month as punishment. Thus begins the tale of the boys' harsh lives in Prison School, a righteous struggle that will ultimately test the bonds of friendship and perverted brotherhood.