Hanae Ashiya is a fifteen-year-old high school student who serves as the main human protagonist. His ordinary life takes an unexpected turn just before his high school entrance ceremony when he encounters a small, fuzzy yōkai. After this meeting, the creature becomes attached to him, and its possession slowly drains his life force, leaving him frequently collapsing and confined to the school's infirmary. Desperate for a solution, he finds a flyer for an exorcist and seeks help from Haruitsuki Abeno, the master of the Mononokean, a tearoom that acts as a gateway to the Underworld for yōkai. The exorcism is successful, but Ashiya cannot afford the hefty fee of one million en, the currency of the Underworld, and is thus forced to work as a part-time employee at the Mononokean to pay off his debt. His family consists of his mother, Nara, who runs a flower shop; an older sister, Chisaki; and his father, Sakae, who has been missing since Ashiya was three years old. This background of having a disappeared father shapes his sensitivity to others who leave without a word.

In terms of personality, Ashiya is defined by his overwhelming kindness, cheerful disposition, and emotional honesty. He is a notorious crybaby with weak tear ducts, often crying easily, whether from joy, sadness, or empathy for the yōkai he encounters. This emotional expressiveness leads others, particularly his boss Abeno, to compare him to a five-year-old child. Despite being occasionally labeled naive or impulsive, he is remarkably persistent and possesses a strong moral compass that prioritizes compassion over rigid rules. He is also known for his meddlesome but well-intentioned nature, which often leads him into trouble as he acts without fully thinking through the consequences. At the same time, he is very sensitive to being ignored by those he cares about and genuinely fears ghosts, even as he grows to love working with yōkai.

His primary motivation evolves over the course of the story. Initially, he simply wants to survive and pay off his debt. However, his innate empathy soon drives a deeper desire to bridge the understanding between the human world and the world of yōkai. He becomes dedicated to making his clients happy, whether they are human or yōkai, and often seeks better, more compassionate solutions to problems than simply exorcising the spirit. This commitment grows so strong that he eventually wishes to continue working at the Mononokean even after his financial debt is cleared.

Ashiya's role in the story is that of a supporting protagonist. While his partner Abeno carries much of the plot's forward momentum with his knowledge and efficiency, Ashiya is the emotional core and the viewpoint character through which the audience experiences the world of yōkai. He is the performer to Abeno's technician, acting in spontaneous and heartfelt ways that, while not always requested by the client, ultimately bring happiness to all parties involved. He undergoes significant development, starting as someone initially fearful of the supernatural to someone who forms deep, affectionate bonds with various yōkai, even risking his own safety to protect them.

His key relationships are central to his growth. His dynamic with Haruitsuki Abeno is the most important. It begins as a forced employer-employee relationship built on debt, with the morose and cynical Abeno often exasperated by Ashiya's naivety. However, it gradually deepens into a partnership of mutual respect and genuine care, with Abeno showing concern for Ashiya's well-being and Ashiya holding deep respect and warmth for his boss. Another critical relationship is with Fuzzy, the very yōkai who originally possessed him. After learning why the creature refused to leave him, Ashiya's annoyance turns into friendship and care, and Fuzzy becomes a loyal companion. He also forms a close friendship with his schoolmate Zenko Fujiwara, whom he helps reconcile with her father. His interactions with powerful underworld figures, such as the legislative Rippō and the human-hating Gyōsei, further define his role as a unique human who is accepted and noticed in the yōkai world.

Notable abilities distinguish Ashiya beyond his inherent kindness. He possesses a latent sixth sense that allows him to see, feel, and communicate with yōkai. He has a strange and specific instinct for finding metal objects, which proves useful on multiple jobs. His most significant and mysterious power is called Influence, an inherited ability that allows him to force yōkai into a state of absolute obedience. This power is a double-edged sword; when activated, his eyes sometimes glow gold, and he can command a yōkai to die. He cannot consciously control this power, and its use typically occurs when he is under extreme emotional distress or feels his life is threatened, often causing him to act unconsciously.