A necromancer known as the Corpse God, cornered by the hero Shagrua Edith Lugrid in a dying fantasy world, casts a reincarnation spell and awakens in modern Shinjuku inside the body of a boy named Polka Shinoyama. With the help of a fixer named Clarissa, he navigates Shinjuku's underworld while piecing together why Polka was murdered and what connects his old world's war to this one.