She is a young 12 year-old girl (13 after chapter 20), abandoned by her mother and a victim of sexual abuse by her stepfather. She has run away from home and is homeless at the start of the series, subsisting on bread crusts she is given at a local bakery under the pretence that they are for the small puppy that accompanies her. She found and named the puppy "Wanta." She ends up living with Kouta and Yuka as her legal guardians. Mayu befriends Nana and tries to take her under her wing.