Kaya Sato, known to her peers and teachers as Kaya-chan, is a kindergarten student at Hanamugi Kindergarten who serves as the central protagonist of the story. On the surface, she has earned a notorious reputation as an infamous problem child, often perceived by adults and classmates alike as a disruptive and inexplicable troublemaker. This misunderstanding stems from a hidden truth: Kaya possesses an incredibly powerful sixth sense and psychic abilities that allow her to see, interact with, and physically destroy evil spirits and malevolent entities that ordinary people cannot perceive.

Her background is deeply tied to the Ebisumori clan, an ancient lineage of priestesses with supernatural powers. Kaya's soul has been infused with the spirit of an ancestor from this clan, a result of her mother, Mirai, using dark family rituals to give birth to her. As a bearer of the Ebisumori blood, she is the latest in a line of firstborn daughters who inherit unique and powerful abilities to combat dark beings. Her power is considered exceptional, even by the standards of her family, with relatives noting that her skills surpassed those of her aunt and grandmother when she was still a very small child.

In terms of personality, Kaya is depicted as being extremely intelligent, fair-minded, and possessing a level of awareness far beyond her young age. She maintains a calm, stoic, and often deadpan expression in her daily interactions, which can make her seem unapproachable or odd to those who do not know her. This demeanor changes dramatically when she confronts a spirit, at which point she reveals an intense, focused, and even fierce presence, fully capable of ruthless violence against the supernatural threats she faces. Despite her tough exterior and the serious nature of her duties, Kaya still exhibits childlike warmth, humor, and a desire for simple pleasures like playing with friends. Her sense of right and wrong is highly developed, and her motivation stems from a compassionate desire to protect her family, friends, and classmates from harm, not from a wish for recognition or praise.

Kaya's role in the story is that of a misunderstood hero and secret guardian. She uses her fists to punch and exorcise the sinister spirits that haunt the school, playgrounds, and even the homes of those around her. However, because her actions appear as senseless outbursts or aggressive behavior to those who cannot see the ghosts, she is frequently scolded and isolated, making her a tragic figure fighting an invisible war alone. She is a child who has learned that no one will believe her explanation for her actions, so she often provides blunt orders or makes excuses without revealing her true rationale. Her isolation is the central conflict of her daily life.

Her key relationships are pivotal to her development. The most significant is with her teacher, Chie Hasumi, who is the first adult to witness a spirit and subsequently believe Kaya. Chie becomes Kaya's first true ally, standing up for her, protecting her innocence, and providing the trust and support that Kaya has been lacking. This bond is a turning point for Kaya, giving her the emotional strength to open up more. Other important relationships include her aunt, Nana Ebisumori, who understands the family's supernatural legacy and tries to support her; her father, Shizuo, who is largely oblivious to the paranormal reality of his life but is a caring parent; her mother, Mirai, whose connection to dark rituals creates a complex and frightening situation for Kaya; and her classmates, who begin to bond with her as Chie's encouragement helps bridge the gap of misunderstanding.

Throughout the story, Kaya undergoes notable development. She transitions from a lonely, isolated child who has resigned herself to being misunderstood to a girl who has an adult in her corner. With Chie's support and the gradual acceptance of her peers, she begins to build genuine friendships and recover some of the joy of childhood that her secret duties had cost her. Her arc also involves confronting the dark truths of her family's past, including the ritual that gave her power and the consequences it holds for her mother, which begins to reveal a larger, more ominous mystery surrounding her existence.

Her most notable ability is her raw physical power to banish evil spirits with a single punch, a method that is both brutally effective and humorously straightforward compared to traditional exorcisms. This power is derived from her connection to the Ebisumori clan's ancestor spirit, which lives inside her. She has been capable of exorcising powerful corrupted spirits since she was a baby, and her abilities are considered the strongest in her family's long history. However, this power comes at a great price. The more she uses her abilities, the more the original ancestor's essence replaces her own, leading to a gradual loss of her humanity. This looming cost adds a deep layer of tragedy to her role as a protector, as her very act of saving others pushes her further away from her own self.