context: the covers of the books they're holding is one of the new summer event Craft Essences called Little Little Bullet, which features Nursery Rhyme, Paul Bunyan, and Jack in a modern mercenary-like setting, with Paul even geared up like a mercenary soldier.
It's a reference to the servent fes event. During the event both Emiya shows up to buy the book but the only reason they want it was because of the details and for the weapons in the story, not because of the lolis. Blackbeard has the honor of doing that instead.
