Nanana's Buried Treasure

Nanana's Buried Treasure takes place on Nanae Island, a man-made island in the Pacific Ocean designed for children's education and training by the Great Seven, led by Nanana Ryuugajou. After being disowned and exiled, high school student Juugo Yama arrives on the island, where he finds the ghost of Nanana Ryuugajou, who was murdered 10 years ago. Nanana had hidden the Nanana Collection, items with unique powers, before her death, and Juugo, with the help of Tensai Ikkyuu and Daruku Hoshino, searches the island for clues to identify her killer.