Hazuki Shiina reigns as Aikoh Academy's premier rhythmic gymnast, celebrated for her exceptional technical precision, elegance, and grace. Hailing from a wealthy family and residing in a large mansion, she initially embodies perfection—talented, beautiful, and universally admired. Her polished performances starkly contrast Hikari Kamijou’s raw, energetic style, fueling a "Technician Versus Performer" rivalry.

Despite competing in gymnastics and vying for Takaaki Ooishi’s affection, Hazuki and Hikari cultivate a supportive friendship. Hazuki openly admires Hikari’s natural athleticism, while Hikari aspires to mirror Hazuki’s refinement. This mutual respect fosters healthy competition, with both encouraging each other’s growth. Hazuki occasionally reveals vulnerability through dizziness or foot injuries during routines, hinting at deeper physical strains.

In the manga, Hazuki’s arc intensifies when leukemia (referred to as aplastic anemia) jeopardizes her gymnastics career. Undeterred, she supports Hikari and trains when possible. Her bond with Takaaki evolves into a romantic engagement, culminating in their joint trip to the 1988 Seoul Olympics to cheer for Hikari. The story concludes with them as a committed couple; her health remains ambiguous, but her spirit endures.

The anime adaptation diverges: omitting her illness, it centers her rivalry with Hikari on athletic and romantic conflict. After an ankle injury sidelines her, she recovers but retires from competition. A flash-forward epilogue shows her coaching young gymnasts. Romantically, the anime implies Takaaki reciprocates Hikari’s feelings, leaving Hazuki’s relationship with him unresolved.

Hazuki’s design reflects her character—her hair styled in a prim bun symbolizing composure, with loose strands subtly hinting at imperfections. She frequently performs in blue or cool-toned leotards, reinforcing her calm, methodical approach.