Koyomi explains that during that debate two years earlier, tension among the students increased until Sodachi proposed a voting to elect the culprit, and while she voted for Koyomi out of her hatred on him, much to her surprise, she herself was chosen by most of the rest of the class. Since then, she stopped coming to school, just appearing to taking the tests while studying at home, while Koyomi stopped trusting people at all, leading to his reclusive life at school until he met Tsubasa, Hitagi and the other girls. Ougi, based on the information she obtained from Koyomi, figures that the true culprit was their math teacher at the time, Tetsujo Komichi, who arranged for her students to glimpse the contents of her test in advance in order to improve their grades and her reputation as a teacher as well, and Koyomi remembers that Tetsujo was one among those who voted Sodachi as the culprit. Now able to leave the room, Koyomi wonders if he was led there by Ougi by purpose, but she denies it. The next day, Koyomi gets himself relieved upon knowing that Tetsujo is on maternity leave and he won't see her again until he graduates. He also looks for the room where he and Ougi were trapped just to find that it is not there anymore, as a sign that the oddity disappeared for good. Just when Koyomi returns to his classroom, Tsubasa appears to stop him from entering, because Sodachi unexpectedly returned to attend classes during Tetsujo's leave, much to his surprise. (thetvdb.com)