Mutio is a member of the aquatic hybrid race created by the scientist Zorndyke, a species often called nereids. She possesses the physical traits of a fish-woman, with long gray hair, red eyes, pointed ears, and distinctive red spots on her skin—a unique coloration that marks her as a rare genetic variation among her kind, who normally display blue tones. Her internal anatomy prevents her from producing speech, but she is highly intelligent and communicates through other means. Like all nereids, she was designed to pilot Zorndyke’s Unigumo fighter craft and was raised to follow orders without question, suppressing her own emotions in service to her creator’s war against humanity.

Mutio’s role in the story begins when her fighter crashes and she is rescued by the human pilot Tetsu Hayami. This encounter confuses her deeply, as she has been conditioned to view humans as enemies. In return for his kindness, she later saves Hayami when he is in danger, and she cares for him by providing food when he is stranded. These interactions cause Mutio to be cast out by her own kind. The hybrid admiral Verg, who leads Zorndyke’s forces, banishes her in a fit of jealousy and rage, and her own sisters brutally beat her for her association with a human. Despite this mistreatment, Mutio retains a compassionate nature. In the final episode, when Verg is mortally wounded by torpedoes, she consoles him as he dies, offering comfort and forgiveness. This forgiving tendency may have been strengthened by her bond with Hayami and her exposure to the Musuca Red Spot, or it may simply reflect an innate empathy.

Throughout the series, Mutio develops from a programmed soldier into an individual capable of independent thought and genuine affection. Her key relationship is with Hayami, whose kindness awakens her capacity for loyalty and care beyond her programming. Her relationship with Verg is more tragic—he abuses her for her connection to a human, yet she still shows him mercy at the end. Her abilities include piloting hybrid submarines, navigating the ocean, and surviving in aquatic environments as a nereid. She cannot speak but conveys emotion and intent through gestures and expressions. Her red eyes and red spots set her apart physically, symbolizing her unique path. Mutio’s story is one of breaking free from programmed obedience, finding connection across enemy lines, and choosing compassion even in the face of rejection and violence.