Well you can see from your picture that there was two books. From the Logical stand point, Kamito wouldn't have two Diaries so that mark it out. I figured it out, because there was another picture that told their intentions. Claire, Rinslet, and Ellis were trying to find out a way to cheer up Kamito because he is a little depress since Est isn't with him during that volume until the end. They decided to get the references from an Erotic books, since they don't know how Kamito or any male feels. Strange Choice if you ask me, though at the end it did help. This picture gave out their intention and what were going on in their heads. Ops never mind, Soji already posted the real reason.
