Whispering Corridors: The Humming (2021)

Eun-hee is hired as a vice principal at her old high school, where strange things take place in the closed down washroom. High school student Ha-young and So-yeon, who used the washroom as their hideout hear humming in the empty washroom, and believe that a ghost exists inside. Ha-young discovers a flowerpot on the stairs and suspect that Eun-hee is somehow linked to the mystery. Suffering from hallucination upon her inauguration, Eun-hee finds a ghastly figured girl in the washroom mirror and begins to believe that the girl was the one who brought her back to this school…