Yukina Himeragi, a middle-school student and Sword Shaman of the Lion King Organization, is entrusted with monitoring Kojou Akatsuki, the Fourth Primogenitor, authorized to neutralize him if he threatens humanity. Her past is marked by a traumatic childhood incident: at six, she narrowly escaped being sacrificed to a Spirit Wolf by sorceresses, leading to her rescue and recruitment by the organization. Raised alongside Sayaka Kirasaka under mentor Yukari Endou, she was secretly groomed as Kojou’s destined blood partner and mate, a strategic measure to control his unstable powers. Posing as a student at Saikai Academy, Yukina conceals her true mission while wielding the Schneewalzer, a divine lance housed in a guitar case. This weapon emits divine vibrations to dismantle magic, though its synergy with her risks morphing her into a Faux Angel—a threat mitigated by a protective ring from Yukari. Her surveillance duty grows complicated as she develops romantic feelings for Kojou, sparking jealousy toward rivals like Kanon Kanase and Astarte, yet she maintains alliances with them. In combat, Yukina summons Shikigami for reconnaissance, channels offensive and defensive enchantments through the Schneewalzer, and temporarily hosts Divine Spirits to amplify her strength, risking her consciousness being overtaken. She inherits the familiar Minelauva Iris from Hektos, augmenting her tactical versatility. Though minimally trained in magic, she employs techniques like Pulsation and Resonant Thunder with precision. Initially socially naive due to her sheltered upbringing—mistaking mundane items for weapons—Yukina gradually navigates human connections, balancing duty with personal bonds. The spin-off *This Is Saikai Academy's Junior High Division* highlights her everyday camaraderie with Nagisa and Kanon, revealing her playful, non-combat persona. Her relationship with Kojou evolves profoundly: becoming his first blood servant awakens his familiar Regulus Aurum, binding their fates. Their shared blood scent symbolizes this union. Future narratives depict their marriage and daughter Reina, cementing her lifelong role as his anchor. Notable traits include aerophobia, a fondness for the Nekomatan cat plushie, fluency in English from accelerated education, and an aversion to mayonnaise. Her physical stats (B76-W55-H78) and consistent presence across all anime seasons, OVAs, and light novels underscore her role as a resolute yet emotionally layered figure navigating duty, love, and self-discovery.