"Children of the Sea" is an anime film adaptation of Daisuke Igarashi’s manga of the same name. The story centers on Ruka, a spirited and curious teenage girl who feels disconnected from her peers and family. During summer vacation, she encounters two mysterious boys, Umi and Sora, who were raised by dugongs in the ocean and possess extraordinary abilities tied to the sea. The boys are under the care of a marine biologist, and their existence becomes intertwined with strange oceanic phenomena occurring worldwide.

As Ruka grows closer to Umi and Sora, she begins to experience surreal visions and dreams that blur the line between reality and the mystical. The narrative delves into themes of interconnectedness between humans and nature, exploring the idea that life on Earth originated from the ocean. The boys’ origins and their connection to the sea become central to the story, as they are revealed to be part of a larger cosmic event involving celestial bodies and the migration of marine life.

The plot intensifies as Ruka, Umi, and Sora embark on a journey to uncover the truth behind the boys’ existence and the mysterious occurrences in the ocean. Their adventure leads them to confront the boundaries of human understanding and the profound mysteries of the natural world. The story culminates in a climactic event where the boundaries between the sea, the stars, and life itself converge, leaving Ruka to grapple with the profound implications of her experiences.

The main characters include Ruka, whose curiosity and emotional depth drive much of the narrative; Umi, the more reserved and introspective of the two boys; and Sora, who is more impulsive and expressive. Supporting characters, such as the marine biologist and Ruka’s parents, provide additional context and emotional grounding to the story. The film’s narrative is deeply rooted in its exploration of ecological and existential themes, blending scientific inquiry with mythological and spiritual undertones.