Keitaro Gentoga is a young man with a strong spiritual constitution, which means he possesses a natural predisposition to attract ghosts and sense supernatural presences. His appearance is notable for the glove he always wears on his right hand, concealing a curse inflicted during a traumatic event in his past. As a result of that incident, nerve endings grow from his hand, serving as a physical reminder of the encounter.

Keitaro's background is defined by this formative trauma. Two years before the story begins, a spiritual encounter in his middle school years led to him and his childhood friend, Eiko Hozuki, being cursed by a malevolent spirit. Overwhelmed by guilt for involving someone he cared about and terrified by the supernatural forces that seem drawn to him, Keitaro became a shut-in, isolating himself from society for an extended period. His re-entry into the world is a gradual process, supported by his family and the persistent encouragement of Eiko.

In terms of personality, Keitaro is characterized by a deep-seated fear and strong dislike of anything related to the paranormal. He is often cowardly and prone to panic in dangerous or haunted situations, especially when the people he cares about are at risk. His social skills have suffered from his long period of isolation, which makes his new role as a private tutor challenging. However, beneath his fearful exterior lies a genuine concern for others. Despite his terror, he is willing to face danger to protect his loved ones. He is also noted for being highly intelligent, as he is able to achieve top scores on university entrance exams despite his prolonged absence from formal study.

Keitaro's primary motivation shifts as the narrative progresses. Initially, his main goal is simply to live a normal life free from supernatural interference. However, his hope for a permanent solution to the curse he shares with Eiko becomes a driving force. When he learns that it might be possible to break the curse, he resolves to cooperate in dangerous activities to achieve that end. This goal is intertwined with his role in the story, where he serves as the tutor for Eiko's younger cousin, Yayoi Hozuki. Yayoi is an elementary school student with an intense obsession with the occult, who seeks to find and confront the spirit that kidnapped her mother. Keitaro's ability to attract spirits makes him a vital, if unwilling, partner for Yayoi, as ghosts tend to avoid her despite her own strong spiritual senses. His role, therefore, is that of a reluctant lure and participant on her dangerous expeditions to haunted locations.

Key relationships define his character arc. His bond with Eiko Hozuki is foundational; she is his childhood friend, his primary support in overcoming his shut-in past, and his girlfriend. Their mutual affection is clear, and they share a unique spiritual link through the identical curse on their right hands. Eiko also has a dark and obsessive side to her personality, which Keitaro is only beginning to understand. His relationship with Yayoi is central to the plot. Initially fearful of her, he gradually develops a partnership with her, learning to trust her methods and becoming committed to helping her achieve her goals while hoping to cure his own curse. His grandmother, a shrine priestess, also plays a crucial background role by helping to suppress his curse and teaching him to maintain his physical and mental health through exercise and meditation, as a healthy body and mind are more resistant to possession.

Over the course of his journey, Keitaro undergoes notable development. He begins as a passive and traumatized individual but gradually works through his trauma, creating personal goals and deciding to actively face his fears rather than run from them. His dynamic with Yayoi evolves as he learns protective techniques and becomes more proficient in confronting supernatural threats, growing from a simple victim into a more capable partner.

Keitaro possesses several notable abilities linked to his spiritual constitution. His primary power is an extremely high level of spiritual awareness and attraction. He acts as a magnet for ghosts, drawing them to him even when other, more powerful psychics cannot. It is later revealed that this is because he naturally produces an immense life force, an energy that is highly coveted by spirits and is said to be comparable to that of a god. This extraordinary vitality is so potent that even the legendary onmyoji Abe no Seimei noted it surpassed his own in his prime. Beyond his supernatural traits, Keitaro is also quite athletic. He follows his grandmother's training regimen to maintain a strong body and mind, which grants him the physical fitness to perform feats such as running long distances while carrying another person, and this disciplined state helps make him less susceptible to spiritual possession.