Aiko Senoo is a transfer student from the Tengachaya district of Osaka, and she speaks with a distinctive Kansai dialect, often using Osaka humor while disliking when others imitate her accent. She has short blue hair and blue eyes, and her athletic, tomboyish nature is balanced by a quick temper and a pragmatic, blunt sense of humor that sometimes masks deeper vulnerabilities. Despite excelling at most sports, she struggles with swimming due to difficult childhood memories of failed lessons with her father. Her parents are divorced, and she lives with her father, who works as a taxi driver; she carries a persistent wish for her parents to reunite. Aiko also harbors a lingering fear of older male authority figures, stemming from a childhood memory of her grandfather’s violence toward her mother. As a witch apprentice, her theme color is sky blue, her fairy partner is Mimi, and her magical tool is a harmonica, through which she casts spells such as "Pameruku Raruku Rarirori Poppun!" She is a core member of the apprentice group alongside Doremi and Hazuki, helping to raise the infant Witch Queen, Hana. Her key relationships include a close friendship with Nobuko Yokokawa, a rivalry with Leon of FLAT4 whom she regularly beats in sports, and a childhood pact to marry Keiichi Harima that resurfaces with mixed feelings. By the end of the series, she chooses to relinquish her magic to remain human, valuing her family and friends.