Asagi Aiba is a high school student at Saikai Academy and a classmate of Kojou Akatsuki. She possesses strawberry blonde hair styled with curled ends and a long ponytail secured by a pink ribbon, complemented by striking pinkish-red eyes. Other characters frequently note her beautiful appearance. She typically wears her Saikai Academy uniform with a sweater and keeps a pink ribbon tied around her left wrist. During moments when she uses her abilities, the edges of her eyes turn red. In middle school, her appearance differed significantly, featuring black hair and non-prescription glasses. Her personality underwent a marked shift during middle school, transforming from a sensible and mature girl into a more flippant, flirtatious, and stylish individual. This change stemmed directly from her developing romantic feelings for Kojou Akatsuki. Asagi exhibits confidence and kindness but becomes easily jealous when other girls interact with Kojou. Despite her typically cheerful demeanor, she reveals a serious and deductive side during critical situations. She displays tsundere-like behavior toward Kojou and openly envies her romantic rival, Yukina Himeragi. Asagi works part-time for the Itogami Island Management Corporation as an expert programmer and hacker, operating under the alias "Cyber Empress." Her hacking abilities intensify when she focuses, characterized by accelerated finger movements and a red glow around her eyes. She can decipher complex codes rapidly, including lost languages, and once hacked an entire corporation's systems while simultaneously fending off rival hackers. Her virtual assistant, Mogwai, aids her in these tasks. For much of the series, she remains unaware that her friends are involved in supernatural activities, despite her work involving the island's systems. She holds the hidden identity of the Priestess of Cain, granting her practical immortality while on Itogami Island, which functions as Cain's altar. This role connects to her programming skills and ties into Mogwai's true nature as an avatar of the island's supercomputers. Meiga Itogami identifies her as the Priestess, noting her inability to be killed by any means while on the island. Her romantic involvement with Kojou forms a core aspect of her character development. Harboring long-standing feelings for him since middle school, she actively pursues him, often encouraged by her friend Motoki Yaze. This leads to moments of jealousy and rivalry with Yukina. In the future, she marries Kojou, and they have a daughter named Moegi Akatsuki. Moegi inherits the Shaula-Viola familiar, one of Kojou's twelve familiars. Asagi later affiliates with the Reich·Der·Morgenrot organization. Kojou is stated to love both Asagi and Yukina equally. Her relationships include a close friendship with Motoki Yaze, who is aware of her feelings for Kojou and frequently supports her romantic efforts. Rin Tsukishima, another friend, often provides her with romantic advice. Asagi's interactions with Yukina evolve from rivalry to cooperation, particularly during crises where they work together to support Kojou. Key events involve her deciphering the Nalakuvera weapon's activation codes under duress from terrorists, showcasing her willingness to protect friends despite moral conflict. She assists Kojou and Yukina in multiple arcs, such as the "Right Arm of the Saint" and "From the Warlord's Empire," using her technical skills to resolve supernatural threats. Her romantic initiatives, like luring Kojou to the art club for a photoshoot in maid attire, highlight her persistent yet playful approach to their relationship.