Hanasaki Ohsuke lost his family in a fire when he was young, and has been alone for the rest of his life. He is taken in by his distant relative, the Sunohara family, and lives with Sunohara's parents, Yoichi, and Yomari's siblings like a real "family." One day, while attending a summer festival at a shrine with Yoichi and Yomari, a mysterious young man, Manju, is attacked by monsters created by killing people...!? A new type of battle horror!!