Yanderain

Poor communication skills, plain, dumb, poor, and gloomy is all that could be said to describe this story's protagonist, Amatarou, who is an unpopular student with nothing special going for him. He begins to have a secret relationship with Shigure Yadori, an honors student in his class.

When it rains, unbeknownst to anyone, the two of them have a secret rendezvous behind the school building. Forced to do vile crimes and hardcore sexual acts by Yadori, the worthless Amatarou begins to develop a superiority complex from having a secret relationship with her and becomes engulfed in her twisted relationship.

[Translated from the official website]