In another world, a hero named Sir Shagrua Edith Lugrid is about to finish off a powerful necromancer known as the Corpse God. However, the Corpse God uses a unique magic skill to reincarnate himself into another world, and ends up in modern-day Shinjuku, in the body of a boy named Polka Shinoyama who just had his throat slit by an assassin. Thinking that this new world could provide the peaceful life he desired in the previous one, the Corpse God takes on Polka's identity and soon integrates himself in the Shinjuku underworld with assistance from a woman named Clarissa and her subordinates.