The ocean isn't a setting in this film, it's a character that knows more than you do. Masaaki Yuasa drowns you in animation and Daisuke Yoshida's soundtrack until the incomprehensible plot stops mattering, because you're not watching a story unfold, you're watching consciousness itself dissolve into something larger. Two boys who swim like they're remembering how to be water will stay with you long after you stop trying to understand what actually happened.

Ruka spends her summer at an aquarium where she encounters two mysterious boys, Umi and Sora, who move through water with an otherworldly grace that seems less like swimming and more like flight. Raised by dugongs, they hear the same strange calls from the sea that she does, and their connection to the ocean runs deeper than the adults around them can fully grasp. As Ruka becomes increasingly drawn into their world, fish begin vanishing from the oceans all over the planet with no explanation. Together the three children explore a dazzling undersea world and learn of a peculiar festival that sea creatures everywhere are preparing for. The boundary between the natural and the supernatural grows thin as Ruka, the boys and the adults at the aquarium find themselves caught up in a mystery far larger than a simple summer adventure.