Denji's life is anything but ordinary. With his pet, Pochita the chainsaw devil, he slays devils to pay off his deadbeat father's overwhelming debt to the yakuza. But when the yakuza betrays him, his dream of a normal life is shattered when he is brutally killed.
Through an extraordinary twist of fate, Pochita is able to merge with Denji and grant him powerful devil abilities, turning him into a chainsaw hybrid. Realising the danger this poses to society, the Public Safety Bureau's elite devil hunter Makima takes him in, giving him a chance to achieve the simple, happy life he always wanted. Armed with his newfound powers, Denji is determined to make his dreams come true.