Shu Itsuki originates from a wealthy family with Kansai roots, primarily raised in a Tokyo villa adapted for his grandfather's care. Neglectful parents led to a close bond with his grandfather, who entrusted him with the antique doll Mademoiselle. Childhood included severe bullying for interests like sewing and dolls, deemed feminine, leaving Kuro Kiryu as his only childhood friend. The loss of Kuro's mother, who supported these interests, compounded his isolation, shaping his later control-focused personality. Physically tall with light pink hair, Shu's attire varies seasonally: light floral shirts and black pants in warm weather; wine-red coats with gold brooches, black turtlenecks, and matching pants in cold weather, always accessorized with a gold watch. Valkyrie stage outfits feature rose-red coats, corsets, and ornate hats with feathers and ribbons. Personality-wise, Shu exhibits perfectionism, neuroticism, and a short temper, though possessing underlying kindness. Trauma from bullying and loss contributed to social difficulties, manifesting as arrogance and isolation at Yumenosaki Academy. He idolizes European art and culture, evident in his creative work and speech patterns incorporating Gratuitous French phrases. Diagnosed in-universe by Natsume Sakasaki, his psychological profile includes PTSD and Other Specified Dissociative Disorder (OSDD-1B). This disorder developed after Valkyrie's public downfall, where lip-synching allegations during a performance caused severe humiliation. Mademoiselle became a dissociative alter ego enabling him to communicate feelings he couldn't express directly. The doll lacks dissociative amnesia and shows distinct personality traits, possibly introjected from Kuro's mother. During Yumenosaki's "War Era," Shu co-founded Valkyrie with Nazuna Nito, reaching the academy's top position through avant-garde performances. His controlling leadership treated members as "puppets" for his artistic vision. Valkyrie collapsed when fine, led by Eichi Tenshouin, exposed their lip-synching mid-performance. Defeat caused Shu's mental breakdown, withdrawal from public life, and increased reliance on Mademoiselle for social interaction. Post-war, he rarely attended classes, surviving expulsion due to administrative leniency toward his talents. He then formed a partnership with Mika Kagehira, a devoted admirer who recognized him from a childhood encounter Shu didn't recall. Their dynamic evolved into mutual dependence: Shu mentored Mika in costume design and performance while Mika provided emotional stability. After graduating, Shu moved to Paris to study abroad, returning occasionally for Valkyrie activities under COSMIC PRODUCTION. His artistic philosophy shifted toward "sublime works of art" as idols, emphasizing emotional expression over perfection. He reconciled with Nazuna, acknowledging past faults in imposing his ideals. Though still meticulous and prone to anxiety, he gradually reduced isolation, attending university and collaborating with global artists. Mademoiselle remained integral to his communication, but he ceased viewing Mika as a "doll," symbolizing growth toward human connection. Relationships with childhood friend Kuro and fellow "Eccentrics" like Wataru Hibiki remained complex, blending resentment with mutual understanding.