Shoudou

Shoudou summary:

In order to approach a girl who works in the entertainment industry, Oga ends up forcing a friendship with Kunie, her younger brother. While going out for fun, they will discover an extreme attraction between each others. Oga finds Kunie masturbating and that leaves him disturbed... but, at the same time, he can't help feeling dragged into the moment. This way, Oga ends up putting his member, which was already hard, into Kunie's mouth...