Mesu Kyoushi 3 ~Inetsu no Gakusha~ Immoral Edition Final by BISHOP - Adult Sex Game

The protagonist, who has amnesia, does not know his identity, but he is able to live comfortably with the aid of his homeroom teacher Touko, and the rest of the school.
However, due to his lack of memories, he lacks dreams and hope, and feels an emptiness that makes him unable to grow attached to anything.
Then by chance, he learns what happened in the school and decides to explore the incident that cost him his memory.