Two ordinary human girls, Ling Haixin and Xia Fan, happen to meet Na Xiya, the princess of the Icy Blue City. The meeting turns them into magic fairies. Beneath the sea lies a mysterious, enchanting place called Hai Ying Bao, the Ocean Castle. Alongside Xiya, the pair take on the duty of protecting both the human world and the world under the sea. Someone is polluting the ocean, and the three set out to learn who is responsible. The result is a magical girl series in 26 episodes, built around transformation and the defense of two worlds.