Oboro Tsukimigusa

A school Prefect trained by Matsukage to adhere to a strict moral code that mostly revolves around protecting Anna from all potentially immoral influences, including mundane items like basketball hoops and toilet paper rolls. Oboro even has this codified under "Five Provisions," which includes the caveat that Oboro cannot interfere if Anna herself exhibits lewd behavior or desires. Surprisingly quick to reverse her position on what is considered "illegal" material when a student protests strongly enough.

Tanukichi later discovers that Oboro is biologically male, though Oboro insists that her gender is whatever the assignment requires.
(Source: Wikipedia)