Miyuki Rokujou, student council president of St. Miator Girls' Academy, upholds order with a stern yet sensitive approach, frequently clashing with Spica’s president, Shion Tōmori, over disciplinary matters. Hailing from an influential family, her tactical intellect and rumored ability to command malevolent spirits cement her reputation as the "Princess of Rokujou Institute."

Her intricate bond with Shizuma Hanazono, Astraea Hill’s Etoile, traces back to their first year as roommates. Initially reliant on Shizuma’s comfort during bouts of homesickness, their dynamic shifted after the death of Shizuma’s former partner, Kaori Sakuragi, with Miyuki becoming her steadfast confidante. Bound by an arranged post-graduation marriage, Miyuki conceals unrequited love beneath unwavering loyalty.

Jealousy simmers beneath her composed exterior as she navigates Shizuma’s grief-stricken attachment to Kaori and growing connection with Nagisa Aoi. Though she prods Shizuma to heal, their strained emotions explode when Shizuma impulsively kisses her—a gesture Miyuki deems taunting, prompting a tearful retreat. Despite personal anguish, she acknowledges Nagisa’s positive influence on Shizuma’s evolution as Etoile.

Adaptations explore her internal conflict through varied lenses: anime highlights romantic longing, while light novels frame her devotion as ambiguously platonic. She strategically manipulates events, such as pushing Tamao Suzumi into the Etoile race to test Shizuma and Nagisa’s bond, believing challenges spur growth.

Privately, Miyuki’s vulnerability surfaces through childhood homesickness and tearful tendencies, memories Shizuma fondly mocks. Shared baths and late-night talks underscore their intimacy, though Shizuma’s teasing occasionally sparks clashes. These moments juxtapose her rigid public persona, painting a tragic figure ensnared by duty and silent yearning.