The fanboy horde was a feature of Chapter 5. They were a large group of fans who gathered upon discovering that their long-missing "idol" Hayasaka Erika was alive, well, and working at MegaGamers. The day after the discovery they surrounded the store, demanding Erika.
Largo believed they were zombies come to worship their idol (He did not discover until Chapter 6 that Erika was, in fact, the idol. He took it in his stride.) He began to take steps to drive them away, culminating in sending his English class against them. In the ensuing chaos wrought by the rabid horde Piro had his nose broken and Largo had his Tokyo Police Cataclysm Division badge revoked by Inspector Sonoda for allowing the event to happen in the first place.