Nei is a ten-year-old girl with short blonde hair and different colored eyes, a condition known as heterochromia. She is one of the central characters in the story, serving as the deuteragonist. Her very existence is a mystery because no children have been born on the colonized Mars for a decade, making her origins unknown. Despite being a real human girl, Nei initially disguises herself as a doll, acting in a stiff, doll-like manner to avoid drawing attention or causing trouble. This behavior has become so ingrained that it has partially become a part of her personality. Layla, the protagonist, saw through Nei's disguise because Layla had lived outside the domed cities in the wild for so long. Nei accompanies Layla everywhere and is the only person or thing that the stoic and emotionally closed-off Layla seems to care for. In turn, Nei follows Layla because she feels she can act like her true self around her, rather than pretending to be a doll. This relationship is the emotional core of the story, with Nei representing a source of warmth and humanity for Layla. Throughout the series, Nei's role is to be both a companion and a catalyst for Layla's journey, as their bond is deeply tied to the larger mysteries of their world. She does not possess any supernatural or combat abilities; her significance comes from her innocence and her connection to Layla. Nei's development revolves around gradually shedding her doll-like facade and embracing her own identity as a real child, even as the dangers of being an unregistered stray doll on Mars threaten her existence.