Hyōka Kazakiri embodies the conscious manifestation of the Imaginary Number District, an aggregation of AIM Diffusion Fields generated by Academy City's espers. Her existence began approximately ten years before the main events, aligning with Kamijou Touma's arrival. Academy City chairman Aleister Crowley deliberately engineered her sentient form to stabilize the volatile Imaginary Number District, designating her as its "Key." Initially manifesting as an unseen presence at Kirigaoka Girls' Academy, she was recorded as a top-ranking student despite never being physically observed. This anomaly led the school to establish a research facility investigating her phantom existence and its ties to the Imaginary Number District. For years, Hyōka observed Academy City from this liminal state, burdened by her influence over the "City of Shimmers"—a dimension formed by AIM fields—and fearing interaction with the physical world. Her appearance resembles a teenage girl with long dark brown hair, golden eyes, and large glasses. She typically wears a school blazer, skirt, and red necktie, later switching to a blue jacket in winter. Gentle, shy, and reserved, she tears up easily. A profound fear of Touma's Imagine Breaker makes her timid around him, stemming from her subconscious awareness that his power could negate her existence. Though anguished by her non-human nature, she exhibits fierce loyalty and self-sacrificing tendencies to protect others, even risking hatred. Her first physical manifestation near Touma's school, orchestrated by Aleister, led her to assist Index Librorum Prohibitorum with a vending machine, sparking their friendship. Meeting Touma during this encounter intensified her fear. While accompanying Touma and Index in an underground mall, they were attacked by magician Sherry Cromwell—manipulated by Aleister to target Hyōka and provoke science-magic conflict. A head injury during the confrontation exposed her hollow physiology and triangular prism core, revealing her non-human identity. Despairing after Sherry branded her a monster, Hyōka was rescued by Touma affirming her humanity. Nevertheless, she later attempted to sacrifice herself as bait against Sherry's golem Ellis to save Index, declaring willingness to embrace monstrosity for her friend. Though she intervened to shield Index from Ellis, her body fractured under strain. Touma reinforced that her capacity for pain and friendship proved her humanity, while Index reaffirmed their bond, halting her self-destructive spiral. Hyōka possesses superhuman strength, speed, and durability. Her AIM-field body lacks conventional vital points and regenerates high-mid level, reconstructing limbs or surviving fatal wounds if her core remains intact. Core destruction is her primary weakness. In base state, she demonstrates wall-level destructive capacity and durability, repelling the multi-ton Ellis. Under external manipulation during global conflicts, she transforms into "Fuse Kazakiri," an artificial angel granting flight and energy projection. This state activates "Artificial Heaven," overlaying the Imaginary Number District across kilometers to impose anti-magic laws that disrupt mana circulation, causing physical backlash in magic users. Destructive capacity scales to island level here, with energy wings extending hundreds of meters for offense or defense via scale-formed barriers. Her development centers on overcoming existential dread through bonds with Touma and Index. Initially defined by fear and isolation, she evolves to accept her dual nature, leveraging abilities to protect others despite personal cost. Her journey underscores themes of identity and belonging.