Houkago 2: Hajirau Hana wa Murete Amaku (2007)

Ryuuichi's first time doesn't go well and he can't get an erection since then. He starts to work at a girl's high school as a janitor but his work attitudes are terrible, so his dismissal is decided. When he is depressed to hear that, he meets Midori. And he gets an erection while talking to her. He can't stand it and rapes her. He has only one month to go so he decides to spend his time at school on raping as many girls as possible...