Hakusen (S04E11)

A new teacher is staying after school grading tests for her class. When she glances out the window, she sees a student in an unfamiliar, old-looking school uniform, laying white powder lines in the schoolyard. The teacher steps outside to issue a warning, but the student is gone, and the white line continues into the school building. So she follows it inside to find the student... (Crunchyroll)