Sodachi Riddle, Part One.Koyomi arrives at his former middle school, accompanied by Ougi, looking for clues regarding Sodachi's hatred towards him. While investigating his former shoe locker, the pair find three letters, and the story then shifts back to the moment when Koyomi is informed by Tsubasa that Sodachi had returned to the school. In the occasion, Tsubasa reveals that Sodachi had made her all sort of questions regarding him and she answered her the best she could. While Tsubasa leaves to inform the homeroom teacher about Sodachi, Koyomi decides to face her directly. In the occasion, Sodachi continuously insults him, claiming that she not only despises him, but that she does so because he has a happy life and does not know the reason why. When Koyomi attempts to calm her down, she hurts him with a mechanic pencil, just when Hitagi enters the room. Fearing for the worse, Tsubasa attempts to hold Hitagi back to no avail but claims that she will not attack Sodachi for injuring her boyfriend. However, Sodachi starts insulting her as well, and after being slapped in the face, Hitagi knocks her down with a punch, before pretending to lose consciousness as well and leaving the situation for Koyomi to resolve. Upon confiding to Ougi about the situation, they conclude that the key to the mystery lies in the middle school where both Koyomi and Sodachi used to study, and because of that they decided to stop there to investigate. Back to the present, the pair find in the letters a map leading to an abandoned house. While exploring the house, Ougi points out that Sodachi must be aware that Tetsujo is the true culprit behind the incident in the classroom two years before, as she decided to return to school just when she left on maternity leave. Despite wary of Ougi's true intentions, Koyomi guides her to the house's attic, where he is about to tell the story of what happened there five years prior.