Shuusaku

The girls' dormitory of Shukusei Music Academy is home to some of the most talented young female musicians in Japan.
In such an elite school, appearances count for everything, but behind closed doors the sounds of screams, whimpers, and dull moans can be heard echoing through the halls. The school handy-man, Shuusaku, cleans up after the girls and picks up all their dirty secrets, which he uses to blackmail them into some very un-ladylike private performances.

Shuusaku may get paid to clean up the building, but his true calling is just the opposite- sexually defiling and disgracing the innocent and high-strung musical maestros.

[From AniDB]