Sumiko Inoue

She is the head of the school's "Disciplinary Committee" who has an uptight personality, where she takes her duty of enforcing the school rules very seriously together with Kyouko (her enforcer) and Masako (her secretary).

It was later on reveled that she is Shibaki's childhood friend.

It is hinted that even though she does exhibits an uptight attitude, she actually wanted to be victimize by Shibaki's perversion. Unfortunately, the latter is pretty much oblivious to it.

(Source: Anime Wow)