Hebikui Tori summary:

From Yaoi Is Life: Hebikui Tori One night in the city, Nijou comes across a man having sex with another man. The next day at school, he runs into that same man, named Chitori, and learns that he's a member of the staff. Nijou can't help but become intrigued by this man who appears to lead two lives - by day, a regular guy on campus; by night, a minx who likes to take it from men in the city. When Chitori drops by his part-time job and they get to talking, Nijou finds himself desiring the other man and becoming attracted to him. It becomes an obsession that he can't shake...