The seven school mysteries, Hanako-Kun the bathroom ghost being No.7. You heard if you walk up to the third stall in the girls bathroom and knock three time saying “Hanako-San, Hanako-San, Hanako-San, are you in there?” Then he will come out. So, you decided to try this yourself

You approach the bathroom stall and slowly begin to knock, a little bit of fear on your face.