Riona Shijō is a focused first-year student in Class 1-3 at Roubai Girls' Academy, assigned seat number 7. After several years playing tennis, she paused the sport for two years to prepare for middle school entrance exams. Upon enrolling at Roubai, she rejoined the tennis club. This hiatus coincided with significant physical development, leaving her with a noticeably mature and curvy figure compared to her peers, a source of self-consciousness and a complex about her body. Embarrassed by her fuller build, she particularly envied classmate Komichi Akebi's slim and athletic physique. This insecurity manifested in smaller, less energetic movements during tennis as she tried to minimize her presence.

She does not live in the dormitory and is sometimes depicted in her personal room with a large pet dog. Her appearance features semi-long hair and a stature that stands out due to its more developed, model-like proportions. Academically diligent, she prioritized exam studies over tennis previously.

Her character arc centers on overcoming body image issues. Participating in athletic festival cheerleading practice alongside Komichi proved pivotal. Observing Komichi's unrestrained energy and determination made Riona realize her own self-consciousness—not physical limitations—was causing her restrained movements. She consciously decided to move with greater freedom and pride during the cheerleading routine, rediscovering her dynamic and energetic style. This experience, combined with support and acceptance from Komichi and classmates, fostered greater self-acceptance. She grew more comfortable with her body, translating into renewed confidence on the tennis court and in daily interactions.

Beyond tennis, she demonstrated athletic versatility by participating in volleyball events during the sports festival. Her personality evolved from initial shyness and a tendency to hide her figure into one marked by quiet kindness and hard work as she learned to embrace herself.