Kazuya Kagami is the central protagonist, a seemingly ordinary middle school boy who is thrust into a hidden world of spirits and exorcism. He lives with his father, Kazuaki, and his older sister, Kasumi, having lost his mother, Kanaka, at a young age. A keepsake from his mother, a cherry blossom-patterned obi, is never far from his side. Unbeknownst to him, this obi is a tsukumogami, an object that has gained a soul after many years, and its name is Kiriha. Kazuya himself is a special existence known as a Taboo Child, a person with a unique constitution that naturally attracts and generates curses. This inherent power played a significant role in his early life and is the reason for his connection to the spirit world. To suppress his overwhelming spiritual energy when he was an infant, his mother transferred ownership of Kiriha to him, sealing his power and stabilizing the curse.

In his daily life, Kazuya comes across as a kind-hearted and mostly friendly individual, though without any particularly distinguishing features at first glance. He is a student at Kamioka East Junior High School and serves as the manager of the Trouble Counseling Department. He possesses a surprisingly strong sense of responsibility and guilt, often feeling a deep obligation to help others, especially when he believes a problem is his fault. This is particularly true regarding his status as a Taboo Child; he mourns the fact that his curse attracts malignant spirits called amasogi and is deeply distressed when innocent people suffer from a curse backlash.

Despite his gentle nature, Kazuya is also a teenage boy with considerable lustful urges, though he possesses an almost superhuman level of self-control. He constantly suppresses his desires, even when subjected to frequent and overt temptations from the female spirits and people around him, earning him a reputation for incredible endurance. He prefers to maintain his current relationships rather than complicate them by acting on his physical impulses. This self-discipline, however, does not make him immune to making foolish mistakes or having perverted thoughts, which often land him in comedic or dangerous situations.

His primary motivation throughout the story is to protect the people and spirits he cares about. He is incredibly brave, often throwing himself into danger without hesitation to fulfill his role as an exorcist and prioritize the safety of others. He holds an immense sentimental value for his partners, like Kiriha and the local guardian deity Kukuri, and seeing them endangered can throw him into a terrifying rage. Furthermore, he carries a heavy burden of guilt regarding the amasogi that are born because of him, driving him to resolve the issues they cause.

Kazuya's most significant relationship is with Kiriha, the tsukumogami of his mother's obi. Their partnership begins reluctantly, with Kiriha forcibly declaring him her servant, but it rapidly evolves into a deep and unbreakable bond. He comes to see her not as a tool, but as an irreplaceable partner and someone extremely dear to him. This respect extends to all tsukumogami; he strongly dislikes anyone who mistreats them. Other key relationships include his childhood friend, Chisato Chikaishi, who has a secret crush on him, and his older sister Kasumi, who acts as a practical guardian and has a pronounced brother complex. His rival and eventual ally, Sunao Sumeragi, also plays a major role in his development. Most critically, his relationship with his own mother, Kanaka, is complex and tragic, as a significant part of his journey involves confronting her and coming to terms with a painful past.

Kazuya undergoes significant development over the course of the series. He starts as a normal boy with no knowledge of the supernatural, forced to rely on Kiriha for protection. Through rigorous training and battles, he grows more confident and skilled. A turning point comes when he learns to perform Ascension, a high-level technique that unifies his mind with his tsukumogami partner, granting him immense power at the cost of physical exhaustion. However, his most profound change occurs after a traumatic incident in which he loses both Kiriha and Kukuri. Initially thrown into despair, he finds a new, steely determination. He vows to destroy the amasogi he created by defeating his mother, becoming far more proactive and serious. He maintains a calmer, more noble disposition, but now fearlessly confronts anyone who threatens his beliefs.

As an exorcist and a Taboo Child, Kazuya possesses several notable abilities. His primary power is his partnership with tsukumogami, originally Kiriha, an obi that can change shape to form shields, enhance his limbs for superhuman strength, or attack as a powerful drill. His true power lies in his nature as a Taboo Child, which causes curses to naturally gravitate toward him and allows him to unintentionally create amasogi from objects. He learns to wield his inherent curse as a weapon, creating a powerful curse backlash. His most advanced technique is Ascension, which transforms his appearance by giving him white hair, ringed irises, and a spiral mark on his forehead, greatly enhancing all of his combat abilities as he achieves perfect synchronization with his tsugumomo. This state is the pinnacle of an exorcist's skill and requires immense training and a deep bond with their partner.