Ami Hyūga is an average high school girl whose world comes crashing down when her brother Yu and his friend Takeshi Sugihara are killed by bullies, led by Sho Kimura. As Ami tracks down Sho, she discovers that the bullies are associated with a ninja-yakuza family. She goes after the clan for revenge, but they brutally overpower her, cutting off her left arm. Ami escapes and seeks shelter with Takeshi's parents, Suguru and Miki Sugihara, two kindly mechanics who fit her with a multi-barrelled machine gun prosthetic. Ami and Miki (who uses a chainsaw) pursue the clan, massacring them one by one. Their victims' families, meanwhile, band together to get revenge.