Shinku is the fifth Rozen Maiden doll crafted by the legendary dollmaker Rozen. Her name means "True Crimson" or "Reiner Rubin" (Pure Ruby), signifying her connection to red roses and noble bearing. She possesses blonde hair styled in twin tails with ringlets, blue eyes, and typically dons a red Victorian-style gown with a matching bonnet secured by a black ribbon and rose brooch.

Originating in the Miniature Garden alongside her sisters, Shinku initially felt jealousy when Rozen created the sixth doll, Hinaichigo. She chose to mentor Hinaichigo instead, forging a close bond and establishing her role as a protective older sister figure. The dolls' harmony shattered when Laplace's Demon imposed the Alice Game, a contest demanding they collect each other's life sources (Rosa Mysticas) to become the perfect doll "Alice." Shinku participated reluctantly, consistently seeking alternatives to battling her siblings.

Her personality blends aristocratic elegance with an imperious, demanding exterior. She treats her human mediums, like Jun Sakurada, as servants, often physically punishing perceived disrespect. Despite this, she develops deep loyalty to Jun, whose influence softens her worldview. She abandons her original motto "To live is to fight," prioritizing protecting others over winning the Alice Game. Contradictions surface in childish obsessions, such as her fervent fandom for the puppet show "Detective Kun-Kun," where she engages passionately with the screen. She also harbors a phobia of cats after one nearly swallowed her wind-up key.

Shinku's history with her sisters is complex. She and the first doll, Suigintou, were once close, but their relationship fractured in "Ouvertüre." Discovering Suigintou incomplete, Shinku pitied her and taught her basic skills like walking and tea-making. When Suigintou later returned complete, Shinku rejected her status as a true Rozen Maiden, calling her "junk" and igniting a centuries-long rivalry. This culminated in Suigintou destroying a brooch Rozen gave Shinku, intensifying their enmity. Nevertheless, Shinku later acknowledges her role in the feud and expresses sympathy for Suigintou's loneliness.

In combat, Shinku manipulates rose petals as versatile weapons—projectiles, shields, or restraints. She wields a cane for close-quarters fighting and commands restoration magic, frequently repairing Jun's broken windows. Her artificial spirit, Holie, augments her abilities.

Across media, Shinku's development focuses on rejecting the Alice Game's brutality. In the manga, she protects the defeated Hinaichigo by taking her as a servant rather than claiming her Rosa Mystica. Later captured by the seventh doll, Kirakisho, she is trapped in the N-field (a plane of consciousness). In "Zurückspulen," an alternate-universe adult Jun constructs a replica body for Shinku, transferring her Rosa Mystica into it. This temporary body has a one-week time limit, forcing a race to rescue her original form from the N-field. Reunited with her primary timeline's Jun, she helps defeat Kirakisho by offering compassion instead of violence, convincing her to surrender her Rosa Mystica.

Shinku ultimately becomes Alice but sacrifices her existence to revive her sisters, entering a comatose state. Her final arc highlights her transformation from a combatant into a unifying force who values familial bonds over perfection.