Yi Han who is a teacher recounts that her school campus becomes quiet after 7:30 PM, and to conserve energy, the lights are dimmed. She avoids working late due to the responsibility of locking up and the eerie atmosphere. One evening, while working late, she went to the office restroom, which uses motion sensors for the lights. After entering a stall, she heard footsteps, the adjacent stall door opening and closing, the sound of clothing, and someone using the toilet. However, upon exiting, she found the restroom empty...