Nitta is a wealthy bachelor who has acquired his money as a minor member of the Yakuza, the Japanese Mafia. One day inside his posh apartment a large egg-shaped container literally materializes out of thin air and falls on his head. Inside is Hina, a strange girl with amazing psychokinetic powers. While Nitta initially wants nothing to do with her, over time they become friends, partly because he's not such a bad person and partly because it's best not to annoy her.
Hina lives in a world where one's status depends on your count--a random tally of the number of times a certain event has occurred to you. Your count can be increased or decreased by other means as well. One's fate if your count reaches zero is to be drawn into 'The Abyss', a fate worse than death. That was what happened to Hina's mother, whose last request was that Hina seek out 'The Legendary Ace', a heroic swordsman who protects young women and clears darkness from the world.