How does this plot for a manga sound?

Ok, a girl named Shannon is completely bored with life and sees no point in living. No one really cares about her, and she doesn't care because everyone bores her. Then she meets another girl named Mandy. She eventually falls in love with her. When she confesses her love, Mandy treats her like a freak. Then Shannon becomes sad and bored again. Well this drives her to insanity. She kills everyone she knows......And thats all I can come up with. I want it to be a psychological horror/. Any suggestions? Any ideas for plot twists or anything? Its a pretty bad plot but....thats all i've all i got.