rumor about the old school staircase where students say the number of steps sometimes becomes 13 instead of the normal count. Because of this strange story, many people believe the staircase is cursed or connected to something supernatural. Kanna becomes curious about the rumor and brings it up to Chuzenji-sensei. As the mystery is investigated, Chuzenji analyzes the situation logically and explains the real reason behind the strange staircase phenomenon, showing once again that the scary rumor comes from misunderstanding rather than an actual supernatural event.