Derek overheard what his new friends were saying, that no one understood them and their suffering. This was nothing new, Derek had been feeling like that for years. But now Derek had a way of making people understand. His black razor blade could change people into emos, essentially allowing them to see the truth about their shitty lives. But having only one "special" razor could only do so much. If they wanted to make people see the truth, it would be easier if they all had "special" razors. So, Derek used the stone to change all the razors belonging to his new friends into "special" black razors, just like his own. Just like the first one he created, once cut a person would become an emo and Derek's friend.
Derek told his friends about this. Jon and Steve were pleased, because they already had their first two targets in mind. Those two girls that passed by them just minutes earlier. The two girls didn't understand them, but soon they would.
Karyn still spied on them, seeing all of this. It certainly made things more complicated. But at least she now knew how people were becoming emos. All she had to do was not get cut by their black razors and she'd be okay.