Ryou Seibai! ~Gakuen Bishoujo Seisai Hiroku~

Private Kibitsu Academy is a prestigious high school that attracts talented students from different backgrounds. Despite most of its students are beautiful females, the school has many problems, one of which is the Gakuseikai, an autonomous group that controls the academy. The protagonist, Hinase Kyouichirou, lives a happy life with his sister-in-law and teacher Saki, until she is assaulted by members of the Gakuseikai and falls into a state of mental breakdown. A school nurse Yamiko Shiroyuki approaches Kyouichirou and invites him to become a member of her team of auditors to defeat the Gakuseikai. Frustrated with his own powerlessness, he agrees to join the team and swear to bring justice to the school.