Kai Etou and Haru Kurabayashi are new crime investigators in the Narcotics Control Department of the Bureau of Health and Welfare. Kai is a 22-year-old man who is weak but generous; he cannot hurt others, even when it is necessary. He becomes a "matori"—a nickname for a criminal investigator in the Narcotics Control Department—to help people break away from drugs. Haru is a hard worker who is self-aware of his aptitudes. He avoids associating himself with Kai because he considers Kai useless and empathetic toward everyone. For their first assignment, Haru and Kai must arrest an infamous drug dealer. During the operation, Kai gets into a fight with the suspect, triggering a "switch" that makes him ruthless and unstoppable. As Kai and Haru struggle to solve drug-related crimes, they edge closer to unveiling the cause of Kai's behavior and his past.