Miki Hashiba is a first-year high school student at a sports-focused school and a member of the school's track and field team, where she competes as a sprinter. Before attending the same high school as Suzuka Asahina, Miki had often encountered Suzuka during track meets and initially disliked her because Suzuka appeared cold and aloof. However, once Miki realized that Suzuka's distant nature stemmed from her perfectionist tendencies and intense dedication to her sport, she developed respect for Suzuka, and the two became close friends.

Miki is defined by her unwavering loyalty to her friends. She consistently prioritizes their well-being and considers friendship the most important thing in her life. She is not afraid to meddle in the affairs of those she cares about, often pushing them to confront their true feelings, especially in romantic situations. While she can be persistent and even insistent in doing so, her actions are motivated by genuine concern. Despite her usually cheerful and outgoing demeanor, she has a sensitive side when it comes to her personal appearance and the way she dresses.

In the story, Miki serves as a confidante and mediator for the main characters. She quickly becomes a good friend to Yamato Akitsuki after he transfers to the school. When Miki initially finds herself attracted to Yamato, she recognizes his deep infatuation with her best friend Suzuka and promptly suppresses her own feelings to avoid complicating their relationships. This selfless decision underscores her commitment to supporting her friends without seeking personal gain. She often helps resolve misunderstandings between Yamato and Suzuka, offering advice or gently scolding one or the other when needed.

Miki's key relationship is with Suzuka, whom she grows to understand and support deeply. She also builds a strong platonic bond with Yamato, becoming a trusted listener and occasional matchmaker. She sometimes clashes with the boisterous Yasunobu Hattori due to their incompatible personalities, but these interactions highlight her patience and good-natured frustration.

As a character, Miki shows steady emotional maturity. She learns to read people's feelings accurately and becomes more proactive in steering her friends toward honest communication. Her development is subtle, grounded in her consistent role as a supportive friend rather than dramatic personal change. In terms of notable abilities, Miki is a skilled sprinter who takes her own athletic training seriously. She is also a perceptive judge of character and an effective communicator, qualities that enable her to mediate friction between others. Her dedication to both her sport and her friendships defines her presence in the series.