Mutio is a member of the aquatic hybrid race created by the scientist Zorndyke, a species of human-fish hybrids often referred to as nereids. She lives in a post-apocalyptic world where the oceans have risen and Zorndyke's genetically engineered creatures wage war against the remaining human population. Mutio is distinguished by her long gray hair, red eyes, and elf-like ears; she is the only member of her species seen with red eyes and red spots instead of the typical blue, a rare sign of genetic diversity. Due to the internal organ structure of her kind, Mutio cannot speak, which makes it difficult for her to convey her feelings and leaves her isolated even among her own people. Her species is naturally intelligent and programmed for strict obedience to Zorndyke, to the point of suppressing their own emotions. However, Mutio develops a strong compassionate side after being saved from drowning by the human pilot Tetsu Hayami early in the story. Though he is supposed to be her enemy, this act of kindness confuses her and plants the seeds of empathy. She later returns the favor by rescuing Hayami when he is in danger and even cares for him and feeds him when he is stranded. These interactions with a human cause her to become an outcast among her own kind. She is banished by Verg, Zorndyke's aggressive admiral, and is brutally beaten by her sisters for her perceived betrayal. Despite this mistreatment, Mutio retains a forgiving nature and in the final episode consoles Verg as he dies from torpedo fire, showing no resentment for the violence he inflicted on her. Her role in the story is that of a bridge between two warring sides, demonstrating that not all of Zorndyke's creations are mindless killers and that empathy can cross the divide between species. Her development is marked by her journey from a silent, obedient soldier to an independent being who chooses compassion over loyalty to her creator. Among her notable abilities are her adaptation to aquatic life, piloting of the Unigumo fighters used by the nereids, and her keen intelligence despite her inability to speak.