Denji's dream is simple: to live a happy and tranquil life while spending time with a girl he likes. However, this is far from reality, as Denji is compelled by the yakuza to slay demons in order to pay off his crushing debts. He is willing to go to any length for money, using his pet devil Pochita as a weapon. Unfortunately, he has outlived his usefulness and is assassinated by a demon working for the yakuza. Pochita, on the other hand, combines with Denji's dead corpse and bestows on him the abilities of a chainsaw demon. Denji, now able to morph sections of his body into chainsaws, uses his new talents to rapidly and ruthlessly murder his enemies. After catching the attention of the official demon hunters who arrive on the scene, he is hired as one of them by the Public Safety Bureau. Denji will go to any length to attain his basic teenage ambitions now that he has the means to battle even the most formidable foes.