Sebastian would be really interesting. He's a demon, so seeing him interact with modern - day society would be full of comical and also rather dark moments. He'd be confused by some things like traffic laws but would quickly figure out how to use his powers to his advantage in a world full of new challenges.
I think Grell could be an interesting character to focus on. His flamboyant and blood - thirsty nature would create some really wild scenarios in the modern world. He might mistake modern horror movies for real - life events and go on a 'hunt' in a movie theater. His obsession with Sebastian would also be amplified in a new setting where there are so many new distractions and potential rivals for Sebastian's attention.
Sebastian would be really interesting. His demonic nature and his ability to adapt to different situations in 'Black Butler' would make him stand out in a crossover. He could use his skills to either help or manipulate the characters in 'Tokyo Ghoul'. His loyalty to Ciel in his own series could be contrasted with his new relationships in the 'Tokyo Ghoul' world, and it would be fascinating to see how he uses his powers to deal with ghouls.
I think Grell would be really interesting. In the real world, Grell's flamboyant and over - the - top personality would create a lot of chaos. He could be a fashion designer or something similar, still with his love for the color red and his chainsaw. His interactions with Sebastian would be hilarious, as Sebastian would be constantly trying to keep him in line while also dealing with the real - world problems.
Sebastian would be the most interesting. His demonic nature and his loyalty to Ciel would bring a whole new dynamic to the Avengers. He could easily outmaneuver most of the villains with his wits and powers.
Ciel and Dean Winchester would be an interesting pairing. Ciel is a young, determined noble who is used to getting his way, while Dean is a tough hunter with a lot of experience. They could learn from each other's ways of dealing with difficult situations. Ciel could teach Dean some of his strategic thinking, and Dean could show Ciel how to handle more physical threats.
Natsu from Fairy Tail would be a great character to focus on. His dragon - slayer magic and hot - headed personality would make for some exciting interactions with the characters from Black Clover. He could have friendly rivalries with the Magic Knights, especially those with powerful fire - based magic. Also, his loyalty to his guild and friends could be a driving force in a story where he has to cooperate with Black Clover characters to save both worlds.
Ron Weasley and Grell Sutcliff. Ron's clumsy but good - hearted nature would be a sharp contrast to Grell's flamboyant and somewhat bloodthirsty personality. Grell could be constantly frustrated by Ron's lack of finesse, while Ron would be completely bewildered by Grell's behavior. Their interactions would add a touch of humor to the crossover fanfiction.
I think Ciel and Lucy would make an interesting pairing. Ciel is this dark, brooding, and calculating character, while Lucy is more of an emotional and warm - hearted person. Their interactions could be really fun to explore, like when Lucy tries to get Ciel to open up more. Another great pairing could be Sebastian and Erza. Sebastian is a powerful demon with his own agenda, and Erza is a strong and no - nonsense mage. They would probably have some intense battles of wills and skills.
Sebastian and Malleus Draconia would be an interesting pairing. Sebastian is a demon with his own set of skills and motives, and Malleus is a powerful fae. Their interactions could be filled with power plays and attempts to outwit each other. They both have an air of mystery and superiority, which would make for some great scenes.
Ciel would be a very interesting character to cross over. He has a dark past and a complex personality. In the Beauty and the Beast world, he could be a catalyst for change. Maybe he could see himself in the Beast and try to help him in ways that the other characters in Beauty and the Beast couldn't. Ciel's experience with dealing with demons and the supernatural could also be used to figure out the mystery behind the Beast's curse. And his relationship with Sebastian would add another layer of complexity to the story.
Angela would be a great character to focus on. She was such a strong and independent character. In a reunion, we could see how she has balanced her career and personal life. Maybe she has traveled the world and has amazing stories to share, and how her relationship with Shawn has either deepened or changed in unexpected ways.