Aisa Himegami wields the esper ability "Deep Blood," lethally attracting 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. Despite the city's advanced research, no solution emerged, leading to her abduction by the Cult of Science and imprisonment at Misawa Cram School. She possesses long, straight black hair styled in a hime cut and frequently wears a traditional miko outfit. Following the Deep Blood Arc, she wears a Necessarius-provided cross necklace. This artifact suppresses her ability by mimicking a "Walking Church" barrier. Typically quiet, blunt, and soft-spoken, Aisa occasionally displays shyness. She shares a gluttonous streak with Index, exemplified when she spent all her money on hamburgers at Macronall Hamburger. 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. However, she perceives herself as lacking individuality compared to peers like Tsukuyomi Komoe, prompting her to frequently read self-help books on building distinctiveness. Despite her reserved nature, Touma observes subtle emotional cues, like a slight curl of her lips when happy. She demonstrates kindness, such as considering distancing herself from Touma’s group to avoid being a liability during her recovery from severe injuries. Her chronological involvement starts in the Deep Blood Arc. Targeted by the alchemist Aureolus Izzard, who promises to seal her ability in exchange for luring vampires, she is rescued by Touma and Stiyl Magnus infiltrating Misawa Cram School. She defends Touma from Aureolus, provoking the alchemist's lethal attack, which Touma negates with his right hand. After this, 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, her role diminishes but remains recurring. During the Sisters Arc, she assists with mundane tasks like treating fleas on Index’s cat Sphynx and comments on Touma’s tendency to attract girls. The Angel Fall incident swaps her appearance with a truck driver. Later, she transfers to Touma’s school and warns him about Kazakiri Hyouka’s link to the "Imaginary Number District." She attempts to contact Touma during Sherry Cromwell’s mall attack without success. At the Daihasei Festival, she bonds with Tsuchimikado Maika. Oriana Thomson mistakes her cross necklace for a magician’s tool, inflicting near-fatal injuries. Stiyl Magnus stabilizes her, and she recuperates in the hospital, receiving visits from Touma and others post-conflict. She appears sporadically in later arcs like the Academy City Invasion and Skill-Out Uprising, featuring minor comedic interactions such as accidentally unhooking her bra strap when Touma helps her during a choking incident. Her background and narrative treatment reflect the author’s stated intent to frame her as "a tragic girl who can never be the female protagonist," contributing to her limited prominence in later storylines.