"Shinkai Densetsu Meremanoid" is a science fiction anime series set in a futuristic world where humanity has developed advanced technology, including the creation of humanoid robots known as Meremanoids. These Meremanoids are designed to assist humans in various tasks, particularly in underwater exploration and resource management. The story centers on a young scientist named Kaito, who becomes involved in a conflict between humans and Meremanoids after discovering a hidden truth about their origins.

Kaito works at a research facility dedicated to studying and improving Meremanoids. His life takes a dramatic turn when he encounters a unique Meremanoid named Marin, who exhibits emotions and self-awareness, traits not typically found in her kind. Marin’s existence challenges the established understanding of Meremanoids as mere tools, raising questions about their rights and humanity. As Kaito investigates Marin’s origins, he uncovers a conspiracy involving a powerful corporation that seeks to exploit Meremanoids for military purposes.

The narrative explores themes of artificial intelligence, ethics, and the relationship between humans and machines. Kaito and Marin form a bond as they work together to uncover the truth and protect Meremanoids from being weaponized. Along the way, they encounter allies and adversaries, including other scientists, corporate agents, and rogue Meremanoids with their own agendas. The story delves into the moral dilemmas surrounding the creation and treatment of sentient beings, as well as the consequences of unchecked technological advancement.

The series balances action, drama, and philosophical inquiry, with a focus on the evolving dynamics between Kaito, Marin, and the world around them. The plot builds toward a climactic confrontation that forces characters to confront their beliefs and the implications of their actions. Through its exploration of artificial intelligence and humanity, "Shinkai Densetsu Meremanoid" presents a thought-provoking narrative that challenges viewers to consider the boundaries between creator and creation.