Klara M. Ruzhkova is a 15-year-old Russian girl, born in Moscow as a product of the secret Nadezhda project to create human-demon hybrids. She and her older sister Leyla were created and raised by scientist Natalia Ruzhkova, who treated them as daughters. The project aimed for human-demon coexistence, but their lives shattered when Valery Kaminski joined. Kaminski manipulated Leyla into aiding his world domination plans while coveting Klara for her superior latent power.

Klara possesses platinum blonde hair and blue eyes. She typically wears a black dress with a red ribbon, a white long-sleeved shirt, white stockings, and black shoes. After awakening her Nadezhda abilities, she manifests white angelic wings, contrasting with Leyla's black wings.

Initially, Klara exhibits extreme shyness and anxiety, stemming from witnessing the destruction of the Moscow Combat Revue near Petrograd. She was present during Kaminski's attack on their airship, causing its crash and killing all members. This trauma erased her memories completely, leaving her unable to recall her past or identity. It also made her fearful of social interaction and distrustful of strangers. Rescued by Seijuro Kamiyama of the Imperial Combat Revue, she was brought to Tokyo for protection.

Joining the Imperial Combat Revue's Flower Division as a trainee, Klara initially clings only to Seijuro for security. She gradually bonds with the members, particularly Sakura Amamiya, who becomes her primary emotional support. Interactions with the Flower Division help her overcome isolation, develop childlike curiosity, and experience milestones like caring for a stray kitten and participating in social outings.

Klara's key ability is power amplification, enabling her to enhance others' spiritual energy, as demonstrated when boosting Claris Snowflake's magic during a demon attack. She also possesses a transformation ability linked to her Nadezhda nature. Emotional extremes trigger dramatic changes: profound sadness causes her left eye to emit energy that revives a 千年櫻 (Thousand-Year Cherry Blossom), while witnessing Leyla's apparent death unleashes a rage-fueled berserk state transforming her into a fiery monster.

Her relationship with Leyla evolves significantly. After regaining her memories, Klara recognizes Leyla as her sister and expresses deep affection. However, she rejects Leyla's belief that Nadezhda are inherently monstrous and unworthy of acceptance. Klara asserts her choice to remain with the Flower Division, demonstrating newfound courage by confronting Leyla about their differing philosophies.

During the final conflict, Klara pilots the Tenjin, a specialized mecha secretly developed by the Imperial Combat Revue, to counter demonic forces summoned by Kaminski. In the climactic confrontation, she combines her mecha with Sakura's to defeat Kaminski, though Leyla's spiritual intervention proves crucial. After Kaminski's defeat, Klara officially joins the Flower Division and participates in their stage performances, symbolizing her full integration.

Klara's core motivations center on protecting friendships and rejecting isolation. She firmly believes in supporting friends when they are hurt or sad, a principle guiding her actions. Her journey concludes with finding belonging within the Flower Division, though her sister's survival and departure to Shadow Tokyo introduce unresolved personal complexity.