Whispering Corridors 6: 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 suspects 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.