Kazuya Kagami is a human teenager designated as a Taboo Child, born to parents Kanaka and Kazuaki Kagami, with an elder sister named Kasumi Kagami. His potent spiritual energy causes curses and malevolent spirits called amasogi to naturally gravitate toward him, a condition originating from his birth where he exhibited strong spiritual presence immediately after Kanaka was assaulted by a mysterious black fog during her pregnancy. Physically, he appears as a light-skinned young boy with short brown hair and brown eyes. Initially described as plain, his body becomes more muscular and defined through combat retraining. He typically wears his school uniform or casual attire like t-shirts and shorts. In dream sequences, a gender-swapped version named Kazumi Kagami features slightly longer hair and small breasts, wearing a female school uniform. Kazuya's personality blends seemingly average traits with profound complexities. He presents as kindhearted and responsible, often burdened by guilt over the amasogi spawned near him, driving his commitment to protecting others even at personal risk. Despite a generally reserved demeanor, he possesses near-inhuman endurance for suppressing perverted impulses, frequently resisting sexual advances from Kiriha, Kokuyou, and Sunao Sumeragi. He consciously avoids sexual relationships to preserve existing emotional dynamics, particularly with Kiriha. His loyalty manifests fiercely when allies are endangered; he nearly murdered an opponent after Kukuri's assassination attempt due to overwhelming rage. Following traumatic events during the Mayoiga Revolt—including the destruction of Kiriha and the death of Kukuri—Kazuya undergoes significant development. Initially plunged into despair, he emerges with heightened determination and a proactive resolve to destroy the amasogi he generates by defeating his mother, Kanaka. His personality shifts toward a more serious and uncompromising demeanor, though he retains core kindness. He carries Kiriha's remains constantly and reacts violently to unauthorized contact with them. His history involves rigorous exorcist training under Kanaka starting in childhood. At age six, he demonstrated exceptional power by spontaneously creating an amasogi from rocks to defend himself, prompting formal training. He later surpassed Kasumi and secretly created a tsukumogami named Azami by imbuing a black obi with curse energy. Azami became deeply attached to him, leading to covert training sessions where Kazuya deliberately spawned amasogi for combat practice. This period included inappropriate childhood experiences where Kasumi manipulated him into non-consensual intimate acts under the guise of education, which he later replicated unknowingly with Kiriha and Kukuri. As an exorcist partnered with Kiriha, the tsukumogami of his mother's kimono obi, Kazuya battles supernatural threats. His combat abilities include Superhuman Physical Characteristics, Cloth Manipulation via Kiriha, and Curse Manipulation. He employs techniques like "Ascension" or "Domination" through fusion with tsugumomo, temporarily amplifying his power to Building level at the cost of post-use paralysis, which he mitigates with curses. His arsenal includes multiple tsugumomo such as Azami, Kyouka, Shinobu, and Mimane, alongside fundamental abilities like Eight Fold techniques for enhanced attacks. He is noted as a combat genius despite average general intelligence.