I was thinking about a new prompt. I haven't gotten very far, though
It doesn't have to be Black Butler if you don't think characters would fit the plot line.
There is a king of something (Hell, Earth, a country, etc) This can be modern or otherwise. The king would be Sebastian. He has a child who's mother died during birth or something (this would be Ciel.) Other than that, I haven't gotten very far. I just thought it would be cool to do something like a royal family.