|Saitama Chainsaw Shoujo
i havent read this but based on the description its what you want
Kirisaki Fumio's just a highschool girl in love...
...but then she finds out that the guy she's fallen for happens to love someone else.
...so she decides to go out and get a chainsaw.
And take it to school.
And then many things happen.
only a short manga but may be worthwhile