Aiko Senoo is a transfer student who originally comes from the Tengachaya district of Osaka and speaks with a distinctive Kansai dialect, a trait that sets her apart after moving to the fictional city of Misora. Her parents are divorced, and she lives with her father, who works as a taxi driver. Throughout most of the series, she deeply wishes for her parents to reconcile and often tries to bring them back together. Energetic and athletic, Aiko is a tomboy who excels in sports and physical activities, though she notably does not know how to swim. She has a short temper and can be blunt, but she is fiercely loyal to her friends and often serves as a steadfast pillar of support. Beneath her tough exterior, she hides vulnerabilities including a fear of older men, which originated from witnessing her grandfather’s violence toward her mother. Aiko becomes a witch apprentice after discovering Doremi’s secret, joining the main group as the third apprentice. Her magic is associated with the color blue, she uses a harmonica as her magical instrument, and her fairy partner is named Mimi. She shares strong bonds with her fellow witches Doremi Harukaze and Hazuki Fujiwara, and she develops notable friendships with Nobuko Yokokawa and the wizard Leon from FLAT4. A childhood friend named Keiichi Harima once made a promise to marry her, a pact she made to hide her inability to swim. In Owarai Gekijō, she appears in comedic chibi-style short skits.