Onani Master Kurosawa (オナニーマスター黒沢) is a manga written by Ise Katsura with illustrations by Yokota Takuma. Thirty-one chapters were published between September 2007 and March 2008.
Onani means masturbation. And that's what this guy is good at. Kurosawa, a middle school student, doesn't have much of a social life and considers the people around him and their petty lives a bother.
Every day after school, he sneaks into the mostly unused girls bathroom on the 3rd floor, and masturbates, a task he considers to be his 'daily duty'. Until one day when he's caught by a girl, who proceeds to blackmail him to help her get revenge on the people who bully her.
As things spin wildly out of control, and Kurosawa begins to realize his changing feelings, things come crashing down and Kurosawa is forced to realize what he really desires in this world.