Myne, born Urano Motosu, was a Japanese college student and aspiring librarian crushed to death by her books during an earthquake. With her dying breath, she yearned for a life immersed in literature, triggering her reincarnation as a frail five-year-old in a medieval-fantasy realm. Afflicted by the Devouring—a lethal condition stemming from excessive mana accumulation—her growth remains stunted, her body weakened, and her existence frequently confined to bedrest. Midnight blue hair, golden eyes, and pale skin lend her a perpetually youthful appearance.

Initially resentful and selfish, Myne raged against her new family, despising her sister Tuuli's vitality and dismissing her parents, Gunther and Effa, as impostors. As Urano's memories solidified, she forged profound bonds with them, idolizing Tuuli and embracing her parents' fierce protectiveness. Driven to recreate books, she harnessed past-life knowledge to invent shampoo, paper, ink, and recipes, partnering with childhood friend Lutz to establish the "Gutenberg" printing workshop.

Her immense mana capacity eclipsed even archdukes' by age seven. Uncontrolled, it intensified the Devouring until High Priest Ferdinand intervened. Becoming his apprentice shrine maiden, she adopted the noble identity "Rozemyne" after Ehrenfest's archduke adopted her to shield her family. Thrust into aristocratic politics, she juggled temple obligations, court schemes, and bibliophilic ambitions. Magical abilities included subconscious blessings, wind shields, and elemental outbursts during emotional peaks. Later, wielding a schtappe, she mastered spells like Schutzaria's Shield.

Resourceful and book-obsessed, Myne prioritized non-violence yet overlooked others' struggles in her pursuits. Compassion extended to retainers, friends, and orphans, whose lives she transformed through education. Threats to loved ones ignited mana-fueled fury—nearly killing the High Bishop for endangering her parents. Evolving into benevolent archduke of Alexandria, she reformed orphanages, championed commoners, and reconciled dual identities. After merging with goddess Mestionora erased her commoner memories, Ferdinand restored them.

Key relationships shaped her: mentoring retainers like Fran and Gil, bonding with book-loving Hannelore of Dunkelfelger, transitioning from a dissolved engagement to Wilfried into sibling camaraderie, and entering a political marriage with Ferdinand while adopting daughter Letizia. Unwavering through all, her purpose endured: creating a world where books belong to everyone.