The protagonist of this work. She enjoys photography and has a close relationship with her sister. While her exact grades are unknown, her dialogue suggests she isn't as academically gifted as Min-young. In Episode 2, she holds the hand of the slimed Min-young and sees a certain place.

Minha's older sister. She was an honor student and works as a counselor at the Slime Center. She turns into a slime at the end of Episode 1, and as she is being taken to the Slime Center in Episode 2, she reaches out with her slime hand to hold Minha's.

The male protagonist. He is a friend from the same school and grade. He first appears in Episode 2. He travels with Minha and helps her.

Lee Jaehee's younger brother. After enduring cold treatment from his father, who only cares about grades, he meets Nam Jihoon and becomes close friends. Later, after Jihoon leaves for personal reasons, Jaehyun can no longer stand his father's constant discrimination between him and his brother. He runs away from home, transforms into a slime right in front of his pursuing brother, and washes himself down a rain gutter; his current status is unknown.

A high school student and the best friend of Lee Jaehyun. He was the only friend to Jaehyun, who struggled with his father's grade-obsessed neglect. He eventually encounters the protagonist's mother, who has fallen into a cult, and acts as a collaborator by infiltrating the cult to relay information to the protagonist.

Yu Min-young's client who lives alone. Min-young visited her frequently to talk. Although she initially seemed displeased by Min-young's frequent visits, she grew fond of her. Later, when the protagonist and Jaehee visit her with the slimed sister, she tells them about her time with Min-young. After they leave, she eventually turns into a slime herself while alone. Fortunately, she returns to normal near the final episode.