Ruka Azumi, a teenager in a secluded fishing village, harbors a deep bond with the ocean, nurtured by her marine biologist parents’ work. Their early divorce fractures her familial ties, fueling simmering anger and alienation. This turmoil erupts when she lashes out at a peer during a game, severing her place in the club. Summers at her father’s aquarium, surrounded by marine life, deepen her affinity for the sea—a legacy of her parents’ careers.

Her solitary world shifts upon meeting Umi and Sora, enigmatic boys with aquatic powers, nurtured by dugongs. Their friendship awakens latent abilities in Ruka, including underwater respiration, and draws her into cryptic marine events. As their bond deepens, she unravels her destiny within life’s intricate web, mirroring the ocean’s boundless connections.

At home, her mother’s alcoholism and emotional distance strain their relationship, a cycle echoing Ruka’s own guarded demeanor. The manga unveils her mother’s lineage of traditional divers and a fraught maternal history, roots that anchor Ruka’s oceanic ties. A fragile reconciliation blossoms with her parents’ renewed unity, marked by a newborn sibling—a beacon of familial healing.

Ruka’s journey arcs from defiant isolation to embracing her cosmic role. A symbolic climb up a once-treacherous hill, her securely tied shoes embodying conquered turmoil, crystallizes her growth. Guided by Umi and Sora and her family’s redemption, she embodies themes of acceptance, life’s cycles, and humanity’s symbiosis with nature.

Stubborn yet introspective, Ruka veils her yearning for belonging behind fiery independence. Her whispered reflections—like marveling at the ocean’s immensity—reveal awe for nature’s grandeur. Through spiritual metamorphosis, her path mirrors universal truths of existence, weaving personal redemption into the cosmos’ eternal dance.