Jin Enjoji, known almost exclusively by his nickname Jiji, is a major character who enters the story as a childhood friend of Momo Ayase. He is a tall, handsome young man with short, dark hair that covers his forehead and sides, and he typically wears dark hoop earrings. His school attire consists of a collared shirt, tie, jeans with a belt, and the school blazer, though he was first seen in a tracksuit.

Jiji's personality is immediately striking and hyperactive. He expresses himself with dramatic movements and exaggerated faces, and he has a habit of ending his sentences with strange verbal tics such as "Fuuuu" or "Fuuuuwaaaatsu". While many girls find him charming and funny due to his good looks and flirtatious nature, the boys, including his new acquaintance Okarun, often find him annoying. Seiko Ayase, Momo's grandmother, sarcastically refers to him as a "genius" due to his moronic and quirky behavior. Despite this extroverted and seemingly carefree exterior, Jiji carries a significant burden.

Jiji and Momo were friends during childhood, and he was unknowingly her first crush. Their friendship ended when he rudely mocked her for following her grandmother's instructions to perform a ritual, and he and his parents subsequently moved to a house in the mountains. Years later, Jiji re-enters Momo's life because of a dire supernatural problem. He began noticing strange happenings around his new home, which his parents dismissed. Eventually, he was directly confronted by a powerful spirit, which he later learns is called the Evil Eye, and his parents fell ill and were hospitalized as a result of the haunting. After three of five hired spirit mediums committed suicide while attempting to exorcise the spirit, Jiji's family was told that Seiko Ayase was their last resort. He contacts her and is permitted to move into her house while his problem is solved.

His primary motivation is to rid his family's home of the Evil Eye and save his parents. This desperate situation drives him to seek out Seiko's help and leads to his temporary stay with Momo. His role in the story expands significantly from a mere client to a core member of the main group. He transfers to Momo's school, becoming a source of romantic jealousy for Okarun, who fears Jiji's history with Momo and his charismatic, handsome demeanor. Jiji is largely unaware of the jealousy he inspires and seems genuinely friendly, even attempting to befriend Okarun. However, his playful and sometimes flippant attitude masks a deeper emotional struggle.

The most transformative event for Jiji is his possession by the Evil Eye, the very spirit that was haunting his house. The yokai sees Jiji as a perfect vessel due to the boy's athletic physique and innately powerful spiritual energy. This possession grants Jiji immense supernatural abilities, but at the cost of his control. When the Evil Eye takes over, Jiji's body becomes a conduit for its grudge-fueled powers. The spirit utilizes Jiji's own skills, such as his love for soccer, transforming them into deadly attacks like the Grudge Ball, a sphere of compressed spiritual hatred kicked with tremendous force. The Evil Eye can also create a nearly impenetrable dome called the Cursed House to trap its enemies. This internal conflict defines Jiji's development; he feels sorry for the lonely spirit and tries to manage its violent urges, a struggle that adds complexity to his character and makes him one of the series' most powerful, yet volatile, fighters.