"Ultramarine Magmell" is set in a world where a new continent, Magmell, suddenly emerges in the ocean, teeming with unknown flora, fauna, and resources. This mysterious land attracts explorers, adventurers, and corporations seeking to exploit its riches, but it is also fraught with danger due to its unpredictable environment and deadly creatures. The story centers on Inyo, a young and skilled "angler" who specializes in rescuing people stranded in Magmell. Inyo is accompanied by his assistant, Zero, a mysterious girl with a calm demeanor and a deep connection to the continent.

Inyo’s work as an angler involves navigating the treacherous terrain of Magmell, using his wits, combat skills, and a unique grappling hook-like weapon to save those in peril. Each episode typically follows a self-contained rescue mission, showcasing the challenges posed by Magmell’s hostile ecosystem and the moral dilemmas faced by those who venture into it. The series explores themes of survival, greed, and the consequences of human ambition as various factions clash over the continent’s resources.

The narrative also delves into the backstories of Inyo and Zero, gradually revealing their motivations and the secrets they carry. Inyo’s past is tied to Magmell in ways that are slowly uncovered, while Zero’s origins remain enigmatic, hinting at a deeper connection to the continent’s mysteries. The dynamic between the two protagonists is central to the story, balancing moments of action with quieter, character-driven interactions.

As the series progresses, the focus shifts from episodic rescues to a broader exploration of Magmell’s origins and the forces at play within it. The introduction of rival anglers, corporate interests, and ancient legends adds layers of intrigue, building toward a larger narrative about the continent’s true nature and its impact on the world. The story maintains a balance between episodic adventures and an overarching plot, offering a mix of action, mystery, and character development.