Rei is an operative working for Section Zero, an ultra-secret division within the Tokyo Metropolitan Police Department that handles criminals who are beyond the reach of standard law enforcement, often through assassination. She has no official identity and is valued for her lethal skills and complete obedience to her superiors. After a successful mission eliminating a corrupt police officer and later a serial killer, Rei attempts to take time off with two friends, including a detective named Oda. During an evening out, the group witnesses a young woman named Yumi Ogasawara deliberately run down and kill her male companion with a car after he rejects her sadomasochistic sexual demands.

Yumi is the daughter of Junzo Ogasawara, a powerful and influential businessman or political figure who uses his connections to cover up her crimes. When the case is officially dismissed as a simple hit-and-run, Detective Oda continues to investigate, putting himself in danger. The corrupt network surrounding the Ogasawara family soon dispatches hitmen to eliminate the witnesses. After Oda is killed and Rei survives an assassination attempt in her own apartment, she realizes her only path to survival is to uncover the truth and bring down the conspiracy, even if it means going beyond Section Zero’s authority.

The investigation reveals that the conspiracy reaches the highest levels of power, ultimately leading Rei to discover that her own superior, the head of Section Zero, is complicit in protecting the Ogasawara family. This betrayal forces her into a violent confrontation where she is captured and subjected to elaborate torture by a sadistic dwarf-like jailer employed by her enemies. Rei eventually escapes, using her intelligence and hidden weapons to turn the tables on her captors. She then abducts Yumi and confronts the corrupt businessman, exacting final vengeance for the death of her friend and the corruption that shielded the guilty. The film concludes with Rei eliminating those responsible, having survived the ultimate betrayal of the institution she served.