When Raku has to buy pet food, Tsugumi accompanies him to see if he is really fit to be Chitoge's boyfriend. However, Tsugumi is bothered by her developing feelings for Raku, so she later seeks advice from her classmates. After being reminded that Chitoge had a first love, Chitoge opens her closet and reads her old diary from ten years ago. When the entries cease, she discovers a key resembling one that could open Raku's locket.