Denji scrapes by in a world where human fears take physical form as devils, working off an inherited debt by hunting them alongside Pochita, a small chainsaw-shaped devil who has become his only friend. Betrayed and left for dead, Denji strikes a bargain that fuses him with Pochita and gives him the power to sprout roaring chainsaws from his body. His transformation draws the attention of Makima, a composed, unreadable officer of the government's Public Safety Devil Hunters, who offers him a place on her squad. Denji accepts for the simplest reasons imaginable: food, shelter and companionship. Teamed with the brooding Aki Hayakawa and the chaotic, self-serving Power, he faces increasingly monstrous assignments while a conspiracy involving devil-aligned assassins closes in around the organisation.
In a near-present world, every human fear manifests as a devil, and the government employs hunters to put them down. Denji, an impoverished teenager crushed by his late father's debt, kills small devils for yakuza handlers with help from his chainsaw-devil companion Pochita. When that arrangement ends in blood, Denji merges with Pochita and is recruited into an official devil-hunting division, hoping the job will finally buy him an ordinary, comfortable life.