Saitama Chainsaw Shoujo

From Horobi no Michi: Kirisaki Fumio's just an ordinary highschool girl in love... ...but then she finds out that the guy she's fallen for happens to like someone else. And then she gets into a fight with a friend... that and various other things are getting her really down... ...so she decides to go out and get a chainsaw. And take it to school. And kill the boy she likes, and herself afterwards. Along with anyone who happens to get in the way.