Miyuki Kasahara is an athletic student at Saint Union Academy with a background in competitive sports. Before transferring, she pursued a competitive track and field career during middle school but quit after a wrongful accusation of cheating ended it. This experience directly influenced her decision to pursue Circlet Bout instead.

She comes from a wealthy family that owns a chain of shoe stores, granting her financial stability without directly impacting her athletic pursuits. Miyuki actively spearheaded efforts to revive Saint Union's declining Circlet Bout club even before Yuka Sasaki's arrival, recognizing both the sport's potential and the school's legacy. Her persistent recruitment of members and lobbying of the student council showcase her determination and leadership.

As a Circlet Bout player, Miyuki wields a double-bladed shuriken, an unconventional choice reflecting her preference for agile combat. Her athleticism translates effectively into the sport, enabling dynamic maneuvers during matches. She exhibits a competitive nature in both practice sessions and official bouts, notably defeating Yuka Sasaki in early sparring sessions while actively pushing her teammates to improve.

Miyuki's development involves learning to balance her competitive drive with teamwork. Initially prioritizing individual performance, she gradually embraces collaborative strategies to strengthen the club's overall effectiveness. Her interactions with Reina Kuroda reveal underlying tensions concerning the club's revival, though she ultimately respects institutional processes while advocating for the team's reinstatement.