Natsuki Minamiya teaches English at Saikai Academy while operating as the high-ranking attack mage known as the "Witch of the Void." She also serves as Itogami Island's security supervisor, monitoring supernatural threats to maintain order. Aware of Kojou Akatsuki's secret identity as the Fourth Primogenitor, she guards this knowledge and occasionally guides his actions. Her true role is guardian of a legendary magical prison, where she functions as "the jailer, the door, and the key." An enchanted sleep halting her aging traps her physical body in perpetual slumber within the prison, sustaining her external presence only through magical illusion. This results in a child-like appearance despite her actual age of 26, leading to teasing nicknames like "Natsuki-chan" from students such as Kojou and Asagi Aiba. Inside the prison, she manifests an adult form with greater height and bust size. Natsuki's history includes a pivotal encounter with Gajou Akatsuki, Kojou's father, after an attack by the Black Death Emperor Faction. Gajou entrusted her with watching over his children while seeking a cure for them, establishing her long-term protective bond with Kojou. During the "Banquet for the Observers" arc, escaped prisoner Aya Tokoyogi stole her memories. In this weakened state, she teleported near the Keystone Gate and instinctively sought out Asagi Aiba, who cared for her under the temporary name "Sana." Natsuki regained her memories and powers after ingesting Kojou's blood during a confrontation with Aya. Personality-wise, Natsuki displays a stern, no-nonsense demeanor as a teacher and authority figure, frequently chiding Kojou for academic failures or inappropriate behavior. Highly intelligent and strategically minded, she leverages her extensive knowledge of Itogami Island's supernatural phenomena to aid allies. Beneath her strict exterior lies a caring nature, shown when she took the homunculus Astarte to a festival. She also exhibits a teasing side, mocking Kojou about his attraction to Yukina Himeragi. Her primary motivation is fostering coexistence between humans and demons. Natsuki's magical abilities center on space manipulation, enabling teleportation, gravity defiance, and temporal travel. She projects magical chains for combat and restraint, creates illusions to misdirect opponents, and wields a dimensional sword capable of defeating powerful entities like Astarte. Her signature ability summons the guardian Rain Gold, a knight in golden armor whose full power remains sealed to prevent catastrophic damage to Itogami Island. Rain Gold has temporarily contained threats like Regulus Aurum. As the prison barrier's creator and sole custodian, Natsuki maintains a self-contained, high-universe-level dimension described as endless. Destruction of her physical body would free all prisoners. Her development highlights resilience. After recovering from memory loss, she continues balancing teaching with guardianship. She participates in critical battles, confronting angelic beings alongside Kojou and Yukina, and remains a strategic pillar during crises like the Alchemist's return. Her commitment to protecting Itogami Island and its inhabitants remains unwavering. In appearance, Natsuki possesses long black hair with distinctive bangs framing her face, blue eyes, and a petite, doll-like stature. She typically wears elaborate gothic lolita dresses with thigh-high stockings and carries a black parasol. During undercover missions, such as investigating harassment on the monorail, she dons the Saikai Academy uniform.