Page in search of a bookmark

While searching for a rare book at her local library, bookworm Chitose Tsujikura befriends part-time librarian and second-year high school student Satsuki Touka. Despite not finding the book, Chitose discovers something else with her new friendship—deeper feelings for Satsuki. On the day before Chitose takes her entrance exams, Satsuki presents her with the book Chitose was looking for. After confidently passing her tests, Chitose eagerly reads the book; yet, all she can think about is returning it to Satsuki so they can talk like they once did. On the first day of school, Chitose goes to Satsuki's classroom to return the book, but she is met with cold stares from the other classmates. Chitose quickly shakes the odd feeling, and when Satsuki appears, she invites her outside. However, Satsuki treats Chitose much differently than she did in the library, coldly talking to her and calling her by her surname. What happened to the girl Chitose loved during their time apart?