The guardian spirit of Haegwang City. However, after a Yakoe (night demon) stole his power, he was reduced to a tiny turtle unable to use any abilities. He is the owner of the training grounds where Sleepground practices. He offers Sleepground a large sum of money to help him reclaim his power. Currently in the form of a blue turtle, he is incredibly old and frequently nags Sleepground for her habit of eating sweets.

A huge fan of Sleepground. He is in the same class as Sudam and serves as the class president.

A ghost owl. Because of this, he becomes invisible to Sleepground whenever she eats something sweet. He acts as Sleepground's friend and assistant; they first met while rescuing children from a cold storage warehouse. He nags constantly, which often annoys Sleepground. In his past life, he was a famous doctor whose surgeries were backed up due to a resort collapse incident. While Dong-hee needed immediate surgery for a seizure, Gakbyeol prioritized saving a young Sleepground whose life was in critical danger, resulting in Dong-hee's death. He later died in a fire and lived in Haegwang, the city of the dead, before drinking forbidden water and becoming a Yakoe in the form of a yellow eagle owl.

Sleepground's rival exorcist. He gained more popularity than her initially by offering cheap services and even free exorcisms for those short on cash. He wears a white suit and performs exorcisms using a custom-made gun. He often mocks Sleepground, asking why she wears such cumbersome clothes or who uses swords for exorcisms these days. While he appears sly and playful, he is actually an inscrutable character who has lost much. He is polite yet irritating. In his human life, he was Gakbyeol's older brother and Dong-hee's father. He resented Gakbyeol for treating Sleepground instead of Dong-hee, leading to the death of his only child. As a Beomhon (wandering soul), he grew to loathe the corrupt soul world and drank forbidden water to become a Yakoe. He aims to turn both the soul and human worlds into a realm for Yakoes and possesses the unique ability to be both a Yakoe and a Beomhon. He is the one responsible for turning other souls into Yakoes.

A famous exorcist in Haegwang City. She performs exorcisms for money and is quite obsessed with it. She is an old friend of Soohyun. When she eats sweets, she loses the ability to see ghosts. She treats Gakbyeol like an assistant and wears special clothing that protects her from spirits. She exorcises ghosts using the Moonlight Sword, an heirloom from her grandfather. Sometimes the sword speaks to provide her with guidance. Despite her greed, she is thorough in her work; almost any problem is solved once she takes the case. She is close to Philip, the owner and operator of the cafe located beneath her exorcism office. Her policy is strictly payment upfront.

An old friend of Sleepground. He is a photographer by profession and reunited with Sleepground while she was exorcising a Yakoe. Since then, he has acted as a bridge, introducing her to Sudam and Deokgae and connecting her to various Yakoe cases. He is Deokgae's older cousin.