Umi Monogatari

Japanese Title: うみものがたり ～あなたがいてくれたコト～

English Title: Sea Story

Plot
The story centers on Marin and Urin, two “pure” sisters who live alongside the fish in the sea, but yearn to be in the world beyond the water and above ground. One day, a beautiful ring falls in the middle of the sea, and Marin and Urin retrieve it. The two decide to leave their waterbound world for the first time to deliver the ring. After an arduous journey, they come across an isolated island where a high school girl named Kanon lives. Accidentally, Urin unleashes a power sealed long time ago in the island, and the only ones who can defeat it are Marin and Kanon, as priestesses of the sea and the sky.