Male Personality: Kind and energetic style. He is in a relationship with Go Baek. He has black hair and black eyes and is scheduled to become a Dokkaebi. He hates the experiments extremely and is friendly with everyone (except the experimenters). He cherishes Go Baek. After Youkai Transformation: Two black Dokkaebi horns grow, his ears become Dokkaebi ears (apricot-colored), and he wields a Dokkaebi club. "..Horns.. are growing from my head..!"

Female Personality: Kind, nice, and diligent. She always carries a white hairpin and bracelet. She has slightly wavy brown hair and deep brown eyes. She wears a necklace and is in a relationship with Kang Cheol. She is scheduled to become a witch. She hates the experiments extremely and is friendly with everyone (except the experimenters). After Youkai Transformation: A black witch hat and a witch's staff. Witch ears will grow. "My ears are growing back..?!"

Male Personality: Energetic and lively. He probably has the highest energy here. He is in a relationship with Taco and cherishes her. He has brownish-black hair and dark brown eyes. He is scheduled to become a demon. He is friendly with everyone (except the experimenters) and hates the experiments extremely. After Youkai Transformation: Dark brown demon horns grow, and a demon horn-shaped tattoo appears under his eye, causing pain as it forms. "..It stings and hurts.. under my eye..!!"

Female Personality: Affectionate, lively, and energetic. She has bluish-white hair and blue eyes. She is in a relationship with Lee Pinggu and wears a blue pendant around her neck. She is scheduled to become a Gumiho. She likes flowers. She hates the experiments extremely and is friendly with everyone (except the experimenters). After Youkai Transformation: Nine Gumiho tails grow, and unique patterns appear on her cheeks. It is said that the area where the tails grow hurts for several days... "..Tails are growing..!!..It keeps hurting where the tails are coming out.."

Male Personality: Lively and energetic, with the second-highest energy level. He is to become a Grim Reaper and is in a relationship with Lee Baeil. He is friendly with everyone (except the experimenters). He has black hair and black eyes with a very slight mix of green and gray. After Youkai Transformation: A Grim Reaper hat appears, and his clothes change into black attire. "..My clothes are changing..?..And what is this hat..?!"

Female Personality: The one who created the Youkai Human Project. She looks kind, but she is actually a cruel person with a bit of madness. She has light purple hair and odd eyes—the right is mint and the left is pink, with plus-shaped pupils. She actually does this work for her parents. While she appears like a normal girl on the outside, she is actually wicked, cruel, and insane.