A second-year middle school student. Though timid and easily discouraged, he is a loyal character who finds courage for his friends. He was originally in the track and field club but quit due to an injury. Along with No Seok-ja and Ahn Miso, he is one of the few sane people. After eating a mysterious fruit, his eyes turn green and he displays superhuman speed.

The most popular girl in Suho's class and an Instagram celebrity. In reality, she is the only daughter of Vates, the leader of the Sanati cult. It is speculated that she possesses great combat power, as even Dr. Bring and Maria kneel before her.

Suho's long-time best friend. Unlike Suho, he is energetic and witty. His dream is to become a YouTuber.

Just as much as Miso, Seok-ja saves the children multiple times. Appearing suddenly in Episode 2, she helps the panicked children escape from the Nurse monster. She informs them that they must enter the room at the very end of the second-floor hallway to find a tablet and deactivate the traps, while also handing over a card key to open the door.

She looked like a monster with multiple eyes, but it was actually a mask. She is extremely violent, aggressive, and possesses physical abilities that far exceed those of a normal human.

While he has knocked out Suho and the others by setting traps, the doctor himself has never directly engaged in hostile actions. He appears with the Nurse almost every time he shows up. He frequently ends his sentences with "This is just like OOO!" and mixes Korean and English. His physical strength appears to be weak.

Unlike Suho's other friends who were helplessly kidnapped and used as test subjects, she plays the role of Suho's helper very well. She saved Suho from the Nurse, used fire to retire the Nurse, and even though she could have escaped alone, she returned to accompany Suho. She claims it's to save her younger sibling, but she seems to help because she has feelings for Suho. Although she displays chuunibyou-like or abnormal behavior, such as shouting magic spells while committing arson, she is surprisingly the most realistic character.