Jin Enjoji, often called by his nickname Jiji, is a major character who serves as a childhood friend and first love of Momo Ayase. He is introduced after his family experiences a series of tragic supernatural events, prompting him to seek help from Momo's grandmother, the spiritual medium Seiko Ayase. After his parents are hospitalized following a failed suicide attempt that Jin believes was caused by a curse, he comes to live with the Ayase family and transfers to Momo's high school.

In terms of appearance, Jin is a tall and athletically built young man with short, dark hair and bangs that fall to his eyebrows. He is generally considered handsome, a trait he combines with a flashy and playful fashion sense that includes dark hoop earrings. His outward demeanor is hyperactive, energetic, and relentlessly cheerful. He is known for his dramatic facial expressions, exaggerated gestures, and strange verbal tics, often acting as a class clown to lighten the mood. While this makes him charming and funny to many of his female classmates, his antics are often found to be annoying by the boys around him.

Beneath this comical and carefree surface lies a more complex and troubled personality. Jin suffers from severe insomnia due to being haunted nightly by a mysterious entity, a burden he hides behind his jokester persona. He harbors deep guilt for having mocked Momo's spiritual rituals during their childhood, a transgression he sincerely apologizes for upon their reunion. He retains a strong romantic affection for Momo, which often leads him to act impulsively and protectively around her, creating a friendly but competitive romantic rivalry with his classmate and friend Ken Okarun Takakura. Despite his struggles, Jin is genuinely caring, brave, and empathetic, showing kindness not only to his friends but also to dangerous supernatural beings, which is a key driver of his character arc.

Jin's role in the story becomes central when an investigation into his cursed home reveals a powerful entity called the Evil Eye, a tragic yokai born from a child who was sacrificed long ago. The Evil Eye is drawn to Jin because of his extraordinarily high reserves of spiritual power and physical potential, qualities that make him a prodigy in the eyes of Seiko Ayase. In a misguided attempt to help the lonely spirit, Jin allows it to possess him, becoming its permanent vessel. This possession transforms Jin based on body temperature: exposure to cold allows the Evil Eye to take over, while warmth allows him to regain control. When possessed, Jin becomes a fearsome fighter whose raw physical strength and spiritual output rival the most powerful attacks of his allies.

Throughout the story, Jin undergoes significant character development as he learns to master his difficult situation. With training from Seiko Ayase, he works to control his involuntary transformations and learns to consciously tap into his own spiritual energy, known as Qi. He develops unique combat abilities based on manipulating grudges and negative human emotions, which he can shape into barriers or compress into powerful projectiles. His signature technique is the Evil Gun, a powerful, focused beam of energy whose attack power is amplified by the act of speaking its name, a method known as "power of words". This combination of natural genius, possession by a powerful yokai, and dedicated training makes him one of the strongest members of the group, capable of channeling immense power that can overwhelm energy-absorbing foes.