This is book number 1 in the Chainsaw Man series.
Chainsaw Man subverts all Shonen tropes with the depiction of its less than perfect and often misguided protagonist Denji. Where most protagonists in this genre are kind to a flaw, Denji is an anti-hero driven by all the wrong reasons making for a refreshingly good story.
— Brenda
Denji is down on his luck, doing everything he can repay a debt to the yakuza - including killing devils with his devil-dog Pochita and selling a few "non-essential" body parts. When Denji gains the power to become a demon at will, things get even messier. Can he survive long enough to reach his ultimate goal - getting physical with a girl?
— Nicholas G.