In the Bureau of Health and Welfare's Narcotics Control Department, Kai Etou and Haru Kurabayashi are new to their work as crime investigators. Kai is a weak but generous 22-year-old man who cannot hurt others, even if necessary. He becomes a "matori"—a nickname for a criminal investigator in the Narcotics Control Department—to help people break away from drugs. Haru, a hard worker self-aware of his aptitudes, avoids associating himself with Kai since he is useless and empathetic toward everyone.

For their first assignment, Haru and Kai must arrest an infamous drug dealer. While at it, 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.

Included one-shot: Volume 5: Drug Hunter (prototype)