The story is set in a world where devils are born from human fears. While usually dangerous and malevolent, humans can form contracts with devils to use a portion of their power. Denji is a young, depressed man, who is attempting to pay back his deceased father's debt to the yakuza by selling several of his organs and working as a devil hunter. Denji also owns a doglike devil named Pochita, which resembles a chainsaw and assists Denji in his work. Denji is tasked by the Yakuza to kill a devil, but discovers a plot by the yakuza to let the devil kill him in return for its aid. Denji is slain and Pochita severely injured, but the two had previously made a deal that allows Pochita to merge with Denji, reviving him as a human-devil hybrid with Pochita's chainsaw ability. Denji kills the devil that killed him and is then approached by a team of governmental devil hunters. As he has now partly become a devil, one of the teams' members, Makima, persuades Denji to become a part of their organization to avoid being hunted by them.