Long ago, humanity lived in the water. However, those that desired land abandoned the sea. They discarded the special raiment granted to them by the sea god that allowed them to survive in the ocean. The sea humans' and land humans' thoughts grew as distinct as the regions they lived, and as time passed, they forgot they were once one people. This will change as Tsumugu Kihara, a land-dwelling human, befriends four students from a community at the bottom of the sea.