I read this a long time ago.
Basically this guy kinda likes this girl. Its a bit like unrequited love. Then all of a sudden, a lot of girls try to rape him and stuff. A guy from the future stops him from having intercourse with them, and tells him if he has sex with any woman other than the one he likes, there will be mass destruction. He also threatens to kill him, but its not that serious.
Genres: Harem, Comedy. Romance?