Chimamire Sukeban Chainsaw

Geeko's weird, creepy, friendless classmate Nero has destroyed all of their mutual classmates, perverting them into her grotesque, monstrous minions. Now she's sending them after Geeko, the only survivor. However, Geeko is setting out, dressed in her skimpy school uniform and armed with a big chainsaw, to end Nero's mad science, no matter how many undead former friends she has to saw down on the way.

(Source: MangaHelpers)