To join, you dont need to know much of Black Butler, but in case you dont know anything, heres a few requirments for your butler:
1: He must wear a suit(I dont care if its green, yellow, red, in pieces or barely there, it must be a suit in some form)
2: He must always follow the orders of is master
3: He must wear the gloves that butlers have(also very important)
This will be updated when I think of other pointers.