Umi Monogatari - S01

Marin and her little sister Urin are seafolk who stumble upon something unusual-a gleaming silver ring lost in the ocean. Marin, warm-hearted and determined to return it, ignores Urin’s warnings about the dangers of the surface world, especially after a turtle elder once vanished there. They travel to the sky world and find the ring’s owner, Kanon Miyamori, who reveals she threw it away after her boyfriend broke up with her earlier that day. Marin argues the ring is too precious to discard, but Kanon tosses it aside again. While searching for it, Urin gets separated and accidentally breaks the seal on a stone coffin, unleashing an evil entity named Sedna. Sensing the danger, the long-lost turtle elder Matsumoto appears and declares Marin the Priestess of the Sea-destined to seal Sedna away alongside the Priestess of the Sky. By chance, Kanon discovers she is the Priestess of the Sky during a battle with one of Sedna’s minions. Though unsure at first, Kanon agrees to join Marin in their mission to stop Sedna and protect the world.