Aisa Himegami possesses the esper ability known as Deep Blood, which lethally attracts vampires. As a naturally occurring Gemstone, her power developed without Academy City's intervention. Ten years before the series, a vampire transformed her entire Kyoto mountain village community; drawn to her blood, they attacked, only to turn to dust along with the original vampire. Seeking to nullify this dangerous ability, she enrolled in Kirigaoka Girls' Academy within Academy City. When no solution emerged, she was abducted by the Cult of Science and imprisoned at Misawa Cram School. She has long, straight black hair styled in a hime cut and frequently wears a traditional miko outfit. Following her rescue, she wears a cross necklace provided by Necessarius that suppresses her ability by mimicking a Walking Church barrier. Typically quiet, blunt, and soft-spoken, she occasionally displays shyness and shares a gluttonous streak, once spending all her money on hamburgers. Her traumatic past fuels persistent guilt and a belief that her power burdens others. After Kamijou Touma saves her life, she develops feelings for him. Perceiving herself as lacking individuality compared to her peers, she frequently reads self-help books on building distinctiveness. Despite her reserved nature, Touma observes subtle emotional cues from her, like a slight curl of her lips when happy. She demonstrates kindness, such as considering distancing herself from his group to avoid being a liability during her recovery from severe injuries. Targeted by the alchemist Aureolus Izzard, who promised to seal her ability in exchange for luring vampires, she is rescued by Touma and Stiyl Magnus. She defends Touma from Aureolus, provoking a lethal attack that Touma negates. Afterward, she stays briefly with Touma and Index before moving into Tsukuyomi Komoe’s residence due to her expulsion from Kirigaoka Academy over the cross necklace. In subsequent arcs, she assists with mundane tasks, experiences an appearance swap during the Angel Fall incident, transfers to Touma’s school, warns him about Kazakiri Hyouka’s link to the Imaginary Number District, bonds with Tsuchimikado Maika at the Daihasei Festival, and is mistaken by Oriana Thomson for a magician, leading to near-fatal injuries from which she recovers in the hospital. She appears sporadically in later conflicts, including minor comedic moments such as accidentally unhooking her bra strap when Touma helps her during a choking incident. Her narrative treatment reflects the author’s intent to frame her as a tragic girl who can never be the female protagonist.