Mayumi Kitajima attends Aota Academy as a student and serves on the girls' volleyball team, specializing in the back-center position. She is recognized as the team's sole nonwhite member. Her cheerful personality coexists with her peripheral role in the team's core dynamics. She shares a close friendship with teammate Mio Matsuda, bonding over mutual interests in doll collecting, anime, and manga.

Physically, Mayumi has light blue hair, blue eyes, and blood type B. She stands 1.73 meters tall with measurements of 83-57-85. Committed to athletic performance, she prioritizes physical fitness through weightlifting exercises at home, enhancing her strength and conditioning for volleyball.