While cleaning out his family's Shinto temple, middle-school student Ushio Aotsuki stumbles upon a hidden cellar which houses a dangerous yokai. The yokai, pinned by a legendary weapon called the Beast Spear for 500 years, attracts many other supernatural creatures to the premises. Ushio is forced to free the creature – whom he names “Tora” – in return for his help in defeating them. Tora, who wishes to eat Ushio but is stalled by the Beast Spear, begins to haunt the boy in the hopes that an opportunity will present itself. However, Ushio's possession of the Spear seems to result in trouble after trouble, and Tora finds himself an unwilling ally to Ushio in his battles against various supernatural foes.