Male, 17 years old. Group A. He has black hair and blue eyes. He is quick-witted and has a personality that loves keeping records.

Female, 17 years old. Group A. A student characterized by a yellow cardigan, wavy light brown long hair, and golden eyes. Although she has a crybaby streak, she doesn't get scared once an exploration begins and acts quite calmly according to the rules even in unexpected situations. She is kind and gentle, with a delicate personality that involves meticulously recording special notes on the map.

Male, 17 years old. Group B. A male student with blonde slicked-back hair and red eyes. For some reason, he is wearing a cast on his right arm, and his top is a gym uniform instead of a school uniform. He hangs out with Nari because they are close. Blunt?

Male, 17 years old. Group B. His mental processing and reasoning abilities are among the highest of the characters. He occasionally shows a surprisingly weak mental state. Judging by his attitude toward his classmates, he seems to be a virtuous leader type who is kind to everyone rather than a charismatic type who rules the class.

Female, 17 years old. Group B. The shortest female student in the class, with thick eyebrows. Unlike Kim Taehyun, who only wears a gym top, she is the only one in class wearing both a gym top and bottom. She is best friends with Taehyun and they are always together.

Male, 17 years old. Group C. A student with black hair wearing a gray hoodie. He is the shortest among the male students. Even in emergencies, he maintains rational judgment with a consistent expressionless face without showing much emotion, but he is depicted as not being a bad-hearted student.

Female, 17 years old. Group C. A female student with brown hair and glasses. She is in charge of the map in Group C. She showed her worth by noticing that the lengths of class time and break time had swapped due to the characteristics of the Black Circle.

Male, 17 years old. Group D. Black hair and black eyes. The delinquent of the group. As a typical delinquent, he engages in deviant behaviors like drinking and smoking, and has a hostile and rough personality. He is close friends with Hyunjun. Fitting his delinquent character, he often acts as the leader of the action. He is a character with two sides, sometimes showing decisiveness.

Male, 17 years old. Group D. A male student with dull light purple hair and purple dead eyes. He wears a white and purple top over his school uniform. Except for laughing while talking to Jeon Seoko, he is almost always expressionless. Unlike Jeon Seoko, who causes conflict with other students through rough language, he shows perfectly normal behavior, such as mediating conflicts between Seoko and others.

Female, 17 years old. Group D. A female student with medium-length gray hair and gray eyes, wearing a zip-up hoodie over her school shirt. Even when the school falls into a hole, she maintains rational judgment with almost no change in expression. Her nickname is Yangso. She is close friends with Seona. It is said that only Lim Seona calls Soyeon by her first name.