What are some interesting plot ideas for Black Butler stories fanfiction?

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.

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.

A great plot could be that the triplets are given the task of protecting a special guest in the Black Butler universe. They have to deal with various threats while also trying to figure out the guest's true motives. They use their combined intelligence and physical abilities to keep the guest safe.

One idea could be Female Ciel trying to navigate the underworld of the Black Butler universe while facing discrimination for being a female in a male - dominated world. She might have to prove herself even more than her male counterpart did.

One interesting plot idea could be that Ciel is a modern - day CEO of a large company, and Sebastian is his highly efficient personal assistant. However, the company is facing a series of mysterious threats, and they have to use their unique skills to solve the mystery. Another idea is that Ciel is a famous detective in the modern world, and Sebastian is his partner. They solve crimes that have a supernatural element to them. A third idea could be that Ciel is a high - school student who discovers that he has some strange powers, and Sebastian, who seems to be an ordinary butler at first, is actually there to guide him in using those powers and protect him from those who would misuse them.

Another plot could involve a real - world detective who stumbles upon the existence of Ciel and Sebastian. The detective is initially skeptical but as he witnesses their abilities, he becomes involved in their world. This could lead to a series of adventures where the detective has to learn to work with the duo from the Black Butler universe to solve crimes that are somehow related to the dark secrets of the Phantomhive family in the real - world setting.