Minami kara no Tegami by define - Adult Sex Game

Kusanagi Kazushi, our main character, steps bravely into the world of online dating websites half out of curiosity and half out of other motives...
It is there that he meets a girl. But when he talks to her, he gets a strange feeling...
And as the distance between them grows shorter, that feeling begins to turn into clear suspicion.
Maybe, just maybe... This girl lives in the same town, and goes to the same school...?