Ami Hyuga is an ordinary high school girl whose life is shattered when her younger brother, Yu, is killed by a gang of ruthless bullies led by the son of a powerful Yakuza boss. Determined to avenge her brother's death, Ami takes on the role of a vigilante and starts hunting down those responsible. However, her quest for justice takes a dark turn when she is captured and brutally tortured, resulting in the loss of one of her arms. Undeterred by her injuries, Ami is rescued by a sympathetic husband and wife pair of mechanics who craft a powerful machine gun replacement for her missing limb.

Armed with her new weaponized arm, Ami sets out with renewed vigor to confront the Yakuza gang and its sadistic leaders. She embarks on a relentless and violent journey, fighting through waves of henchmen and encountering various bizarre and deadly enemies. As she gets closer to the heart of the criminal organization, she uncovers deeper layers of corruption and faces increasingly gruesome challenges. Along the way, Ami must reconcile her desire for revenge with the need to preserve her own humanity amidst the chaos and bloodshed enveloping her world.