Yuuutsu Kyoushitsu

Yuzuru Miyahara hated his classmate, Naofumi Sasame. Sasame was mean, sly and always on his high horse. Miyahara had been a victim of his bullying since they were kids. One day, Miyahara finds Sasame's weakness. He starts using it as blackmail and sexually abusing him.

[Translated from DLsite]