Kasumi Iida serves as a supporting character. She possesses brown hair cut to neck length and green eyes, visually marked by a headband, midriff-baring attire, and opera gloves.

Affiliated with Takamori Academy, Kasumi ranks among its top Circlet Bout players, establishing her as a formidable competitor. Her participation gains significance during a practice match against St. Union Academy, where she faces Yuka Sasaki, an inexperienced yet unexpectedly skilled transfer student. Kasumi's established prowess suggests a predictable outcome. However, strategic insights provided by Yuka's AI-enabled bracelet during the bout enable Yuka to execute a swift countermove, resulting in Kasumi's unexpected defeat.

This loss to a relative newcomer generates significant surprise among spectators and competitors. It directly contributes to Yuka's rising reputation as a potential emerging force in Circlet Bout. The event also draws the attention of nationally top-ranked player Chikage Fujimura, who observes Yuka's developing capabilities.