In the mid-21st century, Tokyo’s criminal underworld is dominated by mafia bosses who have undergone ether enhancement surgery to become beings known as Demon Lords. To counter this threat, the government sanctions bounty hunters called Braves, who temporarily amplify their own ether abilities with a drug called E3 and are legally permitted to kill. The story follows a lone wolf Brave known as the Reaper, Yashiro, who lives a dissolute life preferring simple pleasures like beer, pizza, and card games over heroics. His cynical, scummy existence is disrupted when a determined high school girl and Brave-in-training named Aki Jogamine barges into his life, declaring herself his apprentice. Shortly after, Yashiro is approached by two more aspiring young Braves—Yukine Indo and Sara Kashiwagi Pendragon—and agrees to train them, but only for a substantial sum of money.

As this reluctant master reluctantly takes on his self-proclaimed disciples, he is drawn into escalating confrontations with powerful Demon Lords, rival Braves, and dangerous criminal organizations. The narrative explores Yashiro’s pragmatic and often ruthless methods as he mentors the idealistic Jogamine, who can read minds under the influence of E3, the combat-savvy Indo, and the delinquent yet sensible Pendragon, who is also the daughter of Arthur Pendragon, the head of the organization that oversees Braves worldwide. Alongside his fellow scoundrels Salt Joe, Ongakuya Ishinō, and the unlicensed Maruta, Yashiro navigates the gritty, neon-lit streets of Tokyo where the line between legalized murderer and hero is almost nonexistent. What begins as a paid tutoring job quickly pulls Yashiro back into the heart of the underworld he tried to leave behind, forcing him to confront his own past and the true cost of being a Brave.