Children of the Sea

Ruka Azumi spends her summer vacation immersed in handball practice, using the sport as an escape from her alcoholic mother, the only person she lives with. After an incident gets her kicked off the team, she searches for something else to fill her time and ends up at the aquarium where her father works. There, she meets Umi, a strange boy who was raised by dugongs and is being studied at the aquarium due to his body's unusual dependence on water. Despite his odd origins, Ruka quickly befriends Umi, and they're soon joined by his brother, Sora, who shares a similarly mysterious connection to the sea. The three of them dive into a mesmerizing underwater world, uncovering secrets about an enigmatic "festival" that sea creatures everywhere are preparing to celebrate.