Aru Ajifu, also known as Al Azif, is the original Necronomicon, the most powerful grimoire in existence, manifesting physically as a young girl with lilac hair and green eyes. Hunted by the clandestine organization Black Lodge for her immense power, she forms a contract with Kurou Daijuji to escape capture. This pact grants Kurou access to her limitless magic, empowering him to fight their enemies.

Her name, "Al Azif," stems from Arabic, referencing nocturnal sounds attributed to insects or demons, historically linked to the fictional Necronomicon in Lovecraftian myth. Initially physically incomplete, she must recover missing pages to regain full strength.

In combat, she enables Kurou's transformation into a "magius," augmenting his physical and magical abilities to superhuman levels while she assumes a chibi-like form. She also serves as the secondary pilot for the Deus Machina mecha Demonbane, synchronizing her powers to enhance its function.

Her personality is direct, bold, and impatient with hesitation in danger. She is perceptive about threats, readily acknowledging superior opponents. Unlike previous users who treated her as a weapon, Kurou's respect fosters fierce loyalty and concern for his safety, evolving into romantic feelings toward him in the anime adaptation.

Throughout her story, she shows compassion and protectiveness, especially in critical confrontations. She becomes emotionally invested in Kurou's well-being and the conflict against forces like the Black Lodge and Master Therion. In certain story routes, her actions critically influence pivotal battles, including interventions across timelines to alter outcomes.

Her existence transcends her function as a grimoire, embodying themes of personhood and autonomy within supernatural conflict. Her interactions and development mark a transition from a tool of power to a sentient entity with personal stakes in the fates of those around her.