Umimonogatari ~Anata ga Ite Kureta Koto~

This is the seabed, reflecting the dazzling sunlight, where pure and innocent sea maidens in human form live alongside fish. A girl named Marin is a sea dweller who lives in the world of the ocean and, like her younger sister Urin, longs for the sky (the surface world). One day, a beautiful ring falls into the sea. To return the ring to its original owner, the sisters Marin and Urin leave the world of the sea for the first time. The two finally arrive at an island surrounded by the sea. There lives a high school girl named Kanon. She is a gloomy girl who has just broken up with her boyfriend and now feels hopeless about her daily life. In fact, Kanon is the very owner of the ring that Marin and Urin are looking for. Marin and Kanon, brought together by fate, soon awaken the mysterious powers hidden within them. Transforming into the "Maiden of the Sea" and the "Maiden of the Sky," Marin and Kanon challenge the "darkness" that covers the world...