In Orario, fearless adventurers band together in search of fame and fortune within the underground labyrinth known as the Dungeon. But Bell Cranel, novice adventurer, has bigger plans than riches and glory; he fights monsters in the hope of having a fateful encounter with a girl. When this happens, it doesn't go exactly as he planned. Thus begins the story of an unlikely pair, a boy and a goddess, both trying to prove themselves, both eager to reach their goals.

Staz is a vampire from the surreal "Demon World", and Fuyumi, an ordinary girl, accidentally wanders into the Demon World through a portal. Subsequently after meeting each other, Fuyumi is killed by a carnivorous plant and turned into a ghost, causing Staz to take responsibility and pledge to help bring her back to life.