A young man decides one day to start killing yakuza. After he kills his first two he gets roped into helping a wannabe gangster and his bumbling underlings to perform a hit. While things work out in the beginning, this young psychopath quickly becomes more trouble than the gang expected. Will they be able to rid themselves of him, or will they be his next victims?

Denji has a simple dream—to live a happy and peaceful life, spending time with a girl he likes. This is a far cry from reality, however, as Denji is forced by the yakuza into killing devils in order to pay off his crushing debts. Using his pet devil Pochita as a weapon, he is ready to do anything for a bit of cash.