Tonton Streaming The Mysterious Class (2021) S1E1 - 우리 반에 귀신이 있어 (There's a Ghost in Our Class)

In a late-night seance, the students of Grade 12 - Class 4 in Boseok Boys' High School discover the possibility of a ghost haunting their classroom. Their homeroom teacher coincidentally falls unconscious in the stairwell.