Miyuki Ōnuma serves as the captain of Fujimi High School's volleyball club, initially establishing herself as a domineering and demanding leader. She rules the team with an assertive, harsh demeanor, particularly toward new members Kozue Ayuhara and Midori Hayakawa, whom she and her associates subject to rigorous trials.

Over time, her character evolves through her interactions with Kozue and Midori. Ōnuma’s selfish exterior gradually softens, transforming her from a bullying figure into a more reasonable and effective captain. She learns to collaborate with her teammates, demonstrating a clear arc of personal growth.

Ōnuma eventually steps away from the volleyball team to concentrate on her academic pursuits and prepare for university entrance exams. Her departure leads to Kozue Ayuhara taking over as captain.

She is distinguished by her brown hair, which she wears in girlish pigtails.

The character also appears in a stage musical adaptation of the series, portrayed by a different performer, though the musical introduces no new background details beyond the original narrative.