Nanana Ryuugajou, murdered a decade ago in her own apartment, still haunts the cheapest room on the artificial island of Nanaejima, the one Juugo Yama rents after his father disowns him and packs him off there. She asks Juugo to find the person who killed her, the only clue a dragon mark on the back of the neck, and he joins the school's adventure club, which is chasing the Nanana Collection: the treasures she turned up while alive, now scattered across the island. This manga retells the light novel's opening stretch with its own art and pacing.