Fushigi no Umi no Nadia: The Secret of Blue Water is one of the several games based on the anime series of the same name. The game assumes familiarity with the story of the anime, taking the player directly into the time frame of late episodes, where Grandis and the jewel thieves have already joined Jean and Nadia on their travels with Captain Nemo on his submarine "Nautilus". Following a dramatic scene that reveals more about Electra's past, the crew is stranded on a mysterious island. Jean, Nadia, Marie, and the lion cub King decide to explore it, and discover an ancient civilization in the process.
The game plays mostly like an interactive comic book or a visual novel, though it does contain adventure elements such as verb commands. However, these commands are usually very sparse, and there are no sub-menus with objects or people to interact with. The game advances linearly, and the player's input is for the most part reduced to choosing between several locations to explore first. There is also a separate quiz mode where the player answers trivia questions asked by characters from the series.