Denji is deprived of having a typical adolescent life and is left with nothing but the enormous amount owed by his absentee father. He kills devils for money that inevitably finds its way into the yakuza’s pockets alone with his pet chainsaw devil, Pochita. All Denji can do is daydream of living a pleasant, straightforward life with scrumptious food and a lovely woman at his side. But Denji’s cruel, premature death is caused by a yakuza act of greedy betrayal, shattering all hopes of him ever finding happiness.
Surprisingly, a long-forgotten contract enables Pochita to join with the dead Denji and provide him demon powers, turning him into a hybrid with the ability to change his bodily parts into chainsaws. Denji’s new skills pose a serious threat to society, so Makima, an elite devil hunter with the Public Safety Bureau, takes him in and allows him to live as long as he follows her orders. Denji gives everything to and fights with all of his strength to bring his idealistic aspirations of a happy existence with a beautiful woman to fruition.