The story rotates around the mysterious place called the "Angel Island", which is somewhere in the ocean seas. On the island of angels there is a kind of mermaids, which can live both at sea and on land. They have a human form, but can breathe both in water and on Earth. The Moon-Princess of this type of mermaid, which lives on the angel island, but is expelled for violating some of her rules. As a punishment, they put it in the sea shell and leave her drift around the sea. Meanwhile, Eyji Kusajara, the son of a rich Japanese family, meets Salge (senior sister of the moon) and tries to reveal the secrets of the angel island.