Black Butler and Beauty and the Beast Fanfiction: What are some interesting plot ideas?

One idea could be exploring the Beast's past more deeply. Maybe a story about his life before the curse, his relationship with his family and how it all led to his current situation.

One idea could be that Belle discovers a hidden garden in the Beast's castle that has magical plants which can talk and offer her advice. Another could be a backstory for the Beast, like how he got cursed in a more detailed and different way than in the original story. For example, he was tricked by a jealous wizard who wanted the castle for himself.

Maybe the Dark Beauty is not truly human but a being from another dimension. She and the Beast have a connection that transcends their different forms. They must figure out how to break the curse on the Beast's castle while also dealing with her other - dimensional nature.

One idea could be a new character coming into the Phantomhive household as a potential mate for Sebastian. This character could be a half - demon with unique powers and a mysterious past. Their presence would disrupt the usual dynamic between Sebastian and Ciel, creating all sorts of interesting conflicts and power struggles.

One idea could be creating a story where a new character arrives at the Phantomhive manor with a special power that Ciel is initially suspicious of but later realizes can be useful in his battles against his enemies. For example, the power to communicate with the dead, which could provide valuable information in their investigations.

Another plot could involve an OC who is a powerful magician from a foreign land. They come to England seeking a powerful artifact that Ciel also has his eyes on. This would lead to a series of battles and negotiations between the OC, Ciel, and Sebastian, with the OC having their own set of goals and motives that might not be entirely clear at first.

One idea could be exploring their past before the events of the main story. Maybe a story about their early training or a secret mission they had to undertake together as kids.

A cool plot for a 'Black Butler' crossover fanfiction might be a crossover with 'Kuroshitsuji' and 'Death Note'. Light Yagami could somehow cross paths with Ciel and Sebastian. Light might see Ciel as a means to an end in his grand scheme of creating a new world order, while Sebastian would be intrigued by Light's Death Note and the power it holds. It would be a battle of wits between them, with Ciel caught in the middle, trying to figure out how to use this situation to his advantage.

Well, you could write a fanfiction where the Black Butler characters are in an alternate universe. For example, a steampunk world. Sebastian could be a mechanic instead of a butler, and Ciel could be a young inventor. Or perhaps a story where Grell becomes Ciel's butler for a while, which would be really chaotic and full of humor. And then there's the idea of a story where the Phantomhive Manor is haunted by a different kind of spirit, not just the usual demons and ghosts that are part of the original story.

One idea could be exploring Pluto's past before he became a demon. Maybe he had a family or a purpose that was lost. Another could be a story where Pluto forms an unlikely friendship with one of the other characters in the Black Butler universe, like Mey - Rin. It could be interesting to see how their different natures interact.