Name: Jung Mina Age: 15 Gender: Female Role: The Quiet Student Personality: Taciturn and rarely shows emotion. She carefully observes the actions and words of those around her. Appearance: Black bobbed hair and calm eyes. Traits: Possesses an exceptional memory, rarely forgetting a place or person once seen. Secret: From the moment the incident began, she felt the voice of the mysterious person sounded strangely familiar.

Name: Yoon Harin Age: 15 Gender: Female Role: The Model Student Personality: Calm, rational, and analytical. She values evidence and facts over emotions. Appearance: Long dark brown hair, glasses, and a neat school uniform. Traits: Has an excellent memory and analyzes the rules and clues of the missions. Secret: She discovers that the rules of the missions given by the mysterious person are related to an incident that happened at the school in the past.

Name: Choi Hyunwoo Age: 16 Gender: Male Role: The Mood Maker Personality: Playful and bright. He makes jokes even in scary situations, but he is actually quite cowardly. However, he won't leave a friend in danger to run away alone. Appearance: Messy brown hair and playful eyes. Traits: Knows the school structure and the location of emergency exits unusually well. Secret: He knows hidden passages in the school that he was never taught by anyone.

Name: Lee Junhyuk Age: 17 Gender: Male Role: The Delinquent Personality: Blunt, cynical, and doesn't trust others easily. However, he is calmer than anyone else in a crisis. Appearance: Black hair, sharp eyes, and a disheveled uniform. Traits: Quick to judge danger and accustomed to acting alone. Secret: He knows that the method of the missions given by the mysterious person is related to a past incident at the school.

Name: Kang Doyun Age: 16 Gender: Male Role: The Athlete Personality: Honest, active, and hot-tempered. He acts before he thinks, but he is the first to step up if a friend is in danger. Appearance: Short black hair, sharp eyes, and an athletic build. Traits: Has great physical strength and excellent initiative. Secret: He witnessed a mysterious person inside the school just before the incident but told no one.

Name: Han Seoyun Age: 16 Gender: Female Role: The Class President Personality: Strong sense of responsibility and cool-headed. She makes calm judgments even in crises and takes care of other students. She doesn't show her own emotions well. Appearance: Long straight black hair, brown eyes, and a tidy school uniform. Traits: Highly observant with strong leadership skills. Secret: She had noticed strange things happening at the school even before the incident began.