Kantarou Ichinomiya is a folklorist and part-time exorcist living in Japan during the Taishō period. He is a man of early to mid-thirties who possesses the uncommon ability to see and communicate with youkai, the supernatural creatures of Japanese folklore. His most defining physical characteristic is that he is an albino, with very pale skin, light-colored hair that ranges from white to a pale blonde, and distinctive red eyes. This appearance, combined with the unsettling nature of his spiritual power, caused him to be ostracized by other people during his childhood.

Kantarou outwardly presents himself as lazy, greedy, and materialistic. He frequently prioritizes discussing his fees before accepting a job and shows a strong interest in financial gain or a good meal. He is also known for procrastinating on his writing deadlines, often to the frustration of his editor, and he may try to delegate his research to the youkai who live with him. This behavior, however, is largely a facade. Underneath this shallow and immature exterior lies a deeply thoughtful, serious, and compassionate individual. He carries the weight of a tragic and lonely past, which includes a deep-seated resentment toward his mother for abandoning the family and possibly using him as a tool for his spiritual powers. As a child, he was bullied and friendless, which led him to find his only companions among the youkai others could not see. This history has left him feeling awkward around crowds of people and most comfortable in the company of youkai.

Kantarou's primary profession is that of a scholar and writer of folklore, but he uses his abilities to help others as a demon-buster. His approach to exorcism is highly unconventional. Unlike typical exorcists who seek to destroy or banish youkai, Kantarou prefers to reason with them. He sees his work as a way to help both the humans affected by a youkai and the youkai themselves. One of his greatest motivations is his long-standing search for the powerful Oni-eating Tengu. He eventually finds this being, names him Haruka, and the two form a deep bond that goes beyond a simple master-servant relationship. While Haruka is his most important companion, Kantarou also lives with Youko, a fox spirit who he has also named. He cares deeply for his youkai family and considers himself skilled at befriending supernatural beings.

Kantarou's role in the story is as a mediator between the human and spirit worlds. He does not fight physically; his skills are entirely spiritual and intellectual. He is a brilliant tactician who is always thinking several steps ahead to manipulate situations to a favorable outcome, a trait that earned him the nickname that is the title of the series. His abilities are rooted in his deep knowledge of Shingon Buddhism, Shinto disciplines, and Japanese mythology. He is a powerful spiritualist with an unusually high level of power that many youkai consider to be on par with their own. His notable abilities include performing complex exorcisms, creating spiritual barriers known as kekkai, using ofuda (paper talismans) and mantras, and calling upon the power of Buddhist deities. His most frequently used technique is the Kuji, a complex and highly effective exorcism skill. He also possesses the unique ability to name a youkai, which creates a binding contract between them. However, he refuses to do this against a youkai's will and has only ever named Youko and Haruka, whom he considers family. Despite his immense spiritual power, he has no combat ability and is largely defenseless in a physical fight, requiring his companions to protect him while he prepares his spiritual techniques.