Fudoutoku na Yami

Fudoutoku na Yami summary:

One day after school, high school student Meguru Shina is ravished in the train station bathroom by Sasakawa, his math teacher. Usually Sasakawa deceives the world with his slightly dirty white coat and teacher’s mask, but in reality he is a man who will stop at nothing to get what he wants.
Starved for love but unable to reveal his weakness due to his own pride, Shina is drawn in by Sasakawa’s sweet words and pleasing techniques. Shina is trapped by s.e.xual desire. Sasakawa burns with jealousy. The two fall deep into the darkness of a corrupting love…