The fact that their birthday have special meanings like, for example Shizuka's birthday 11/1 which is the same day as "book day" in japan instead of just creating random meaningless birthday dates proves how devoted they are to the manga.
This chapter is just raw chaos. And it will only escalate from here.
"Did I just get mixed up in some seriously deranged gang, here?"
Well, I'm not going to say no...