Ami is a tough but otherwise average high school girl, trying to lead a normal life. Her world comes crashing down when her brother and his friend are killed by ruthless bullies. As Ami tracks down the ringleader, she is surprised to discover the bullies' association with a sinister ninja yakuza family. When she tries to take her revenge, she soon finds herself in over her head and minus her left arm. Barely surviving, Ami escapes and seeks out shelter from two kindly garage mechanics. They take pity on her, fitting her with a high-powered machine gun where her arm used to be. She then teams up with the chainsaw-wielding mother of her brother's slain friend and together they unleash an unholy, non-stop, over-the-top kill fest against the equally creative machinery (drill bra, flying guillotine) of their relentless ninja enemies.