A secret unit within the Tokyo Police Department known as Division Zero operates so far outside official records that few people even within the force know it exists. Charged with eliminating Japan's most dangerous criminals through any means necessary, this clandestine branch deploys agents who have no legal identity. Rei is the unit's sole female operative, a deadly and seductive assassin who uses her body as a weapon as readily as her firearm. Her latest mission begins when she poses as a prisoner to help a beautiful inmate named Yuki escape from jail. Yuki is a cold-blooded killer who lures powerful men into sexual encounters before murdering them. After Rei executes Yuki's accomplices following the breakout, a chance encounter puts her on the radar of Hayami, a principled but curious police inspector who witnesses one of her hits. As Hayami becomes obsessed with uncovering the truth about the mysterious woman in the red overcoat, he finds himself drawn into a web of corruption that reaches from the police department to the American military. Rei's investigation reveals that Yuki is part of a larger criminal network trafficking confiscated drugs, with ties to corrupt officers and government officials. While Hayami struggles to reconcile his growing attraction to Rei with his duty to expose her, Yuki continues her rampage, setting a trap that forces Rei to confront her own blurred lines between justice and vengeance. The final confrontation strips away Rei's armor completely, leaving her exposed and forced to choose between her mission, her growing humanity, and her survival.