Akira Asai is a human teenage girl possessing a noticeably voluptuous build and short hair depicted variably as black or dark brown. Her eyes are typically portrayed as black with tiny pupils and no visible iris, though sometimes illustrated amber on volume covers. She routinely wears her school uniform: a long-sleeved white shirt, striped tie, grey skirt, and brown loafers, adding a grey blazer in cold weather. For physical education, she dons a dark track jacket with partially white sleeves and black shorts, often tying her hair in a ponytail. At home, she prefers sleeveless shirts and pajama shorts. Her physical appearance, especially her chest size, occasionally draws comment from other characters. Akira maintains a disciplined routine, sleeping at 8 PM and rising as early as 4 AM for pre-school walks. She approaches education seriously, adhering strictly to school protocols despite finding school life boring and alienating. Her personality blends maturity and perceptiveness with underlying gloominess and snark. Once lively and talkative as a child, she grew increasingly withdrawn due to dissatisfaction with social interactions, a lack of meaningful connections, and an unfulfilling home environment dominated by monotonous routines. She exhibits signs of depression, having been "unable to bring herself out anymore," and reacts negatively to overly positive statements. Akira displays a carefree yet protective attitude toward close friends, acting as a guardian figure, particularly toward Kou Yamori whom she views like a younger brother. She can become hot-tempered and physically assertive when irritated by those close to her but supports their unconventional choices. She harbors strong distrust of vampires, typically feeling uncomfortable around them, though she accepts their existence when confronted with evidence. Her background centers on a long-term childhood friendship with Kou Yamori and Mahiru Seki. She lived in the same apartment complex as Kou and frequently watched over him, noting his isolationist tendencies. Their friendship waned after sixth grade until a chance nighttime reunion years later, prompted by Kou leaving a walkie-talkie on her apartment mailbox—intended as a random game—which she discovered and kept, hoping he would contact her. She partly blamed herself for Kou leaving school, believing her advice to Sakura Asakura to confess to him indirectly caused his harassment. Akira treasures her relationships with Kou and Mahiru, describing them as unlikely to find similar friends again. She felt jealousy when Mahiru first had a proper conversation with Kou post-reunion but later bonded with Mahiru over shared traits and mutual care for Kou. Her development involves navigating Kou’s nocturnal lifestyle and goal to become a vampire. Though skeptical and unnerved by vampires, she supports Kou’s decision, promising to let him drink her blood once transformed to prevent his suffering. She reconnects during his night walks and befriends Nazuna Nanakusa despite initial disapproval, eventually acknowledging the genuine nature of Kou and Nazuna’s relationship. When Mahiru becomes involved with the vampire Kiku Hoshimi, Akira actively intervenes, traveling to Hokkaido to confront him. Frustrated by Mahiru and Kou’s lack of honest communication during their reunion, she physically forces them to confront their feelings. After Mahiru chooses to become a vampire with Kiku, Akira waits for his return, breaking down when Kou confirms his death. Her dynamic with Kou evolves as he becomes a half-vampire; she grows somewhat fearful of his personality changes but maintains their close bond, later teasing him about vampire bite marks during a group trip. She consistently prioritizes her friends’ well-being, even when it conflicts with her discomfort or societal norms.