For Kuroshitsujii / Black Butler fans...

the demons don't have to become your butler/maid they become whatever you tell them. Ciel told Sebastian to be his butler because based on Ciel's social standing it would just have been the most convenient. I can assume that they would go to the world of the demons and try to solve that crap out. I would think that the demons appear when a human "summons" them I guess, but they make a contract only if they want their soul so I guess Ciel just won't make any contracts and just let some other demon take the person. But yea I thought what you said for a while..... Also I would think that Ciel has to do it because they commanded him to do it not to tell someone else to do it. But yea I get where your coming from.

I don't think Ciel is planning on entering a contract with a human since Sebastian can give him all the souls he needs.

And also, I don't even follow that ending since I read the manga before I watched the show, so I personally don't pay much attention to the anime.

That's just my view on it.