Ruka's parents are no longer together, and her father works in an aquarium. When Umi and Sora, two boys who were raised in the sea by dugongs, are brought to the aquarium, Ruka feels drawn to them and starts to realize that she has the same kind of supernatural connection to the ocean that they do. Umi and Sora's special power seems to be linked to strange things that are happening more and more often, like sea creatures showing up in places where they don't belong and aquarium animals going missing all over the world. But the boys' powers and the strange things that keep happening aren't clear, and Ruka is drawn into finding out what's going on with her new friends.