Juugo Yama, a high school student who has been disowned and banished by his family, lands on this island, relieved to be free of his father. When he moves into his new room, he encounters the spirit of Nanana Ryuugajou, who has been linked to the island since her unsolved death ten years before. Nanana informs Juugo that, right before her death, she buried things with enigmatic and unique properties all across the island, which are known as the Nanana Collection. With the help of self-proclaimed "Master Detective" Tensai Ikkyuu and her cross-dressing maid Daruku Hoshino, Juugo sets out on his hunt for evidence that would lead him to the person responsible for her death.