Mayu is a young teenage girl who runs away from an abusive home and becomes homeless at the beginning of the series, eventually finding a new family at the Maple House. She is abandoned by her mother and suffers sexual abuse at the hands of her stepfather, and when she confides in her mother, she is slapped and treated not as a victim but as a rival for her stepfather's attention. This betrayal drives her to flee home and live on the streets, where she survives by collecting bread crusts from a local bakery under the pretense that they are for her puppy, Wanta, whom she found and named after running away. At the start of the story, Mayu is encountered in the rain with Wanta in a makeshift shelter, and she later crosses paths with Kouta and Yuka at the inn. Despite her initial shyness and reluctance to trust others, she eventually accepts their care and comes to view Kouta and Yuka as her parents, seeing them as far better guardians than the family she left behind. She also befriends Nana, a diclonius, and tries to take her under her wing, teaching her how to survive and navigate daily life. Mayu helps around the Maple House with chores and, over time, begins to mature emotionally, even gently teasing others as her confidence grows. She carries the deep emotional scars of her past, but her motivations center on finding safety, belonging, and a sense of family. In the story, Mayu serves as a secondary character who represents the perspective of an innocent, normal human caught in the violent world of diclonii, and her presence provides a grounding, emotional contrast to the supernatural conflicts. She does not possess any special abilities, but her resilience, empathy, and hard-won savvy allow her to survive and grow. Her relationships with Kouta, Yuka, Nyu, and Nana deepen over time, and she becomes a stable, caring member of the household. Her development is marked by her gradual recovery from trauma and her ability to trust and love again, culminating in her acceptance as a permanent part of the family at the inn.