In this fanfic, Ciel could potentially be sorted into a Hogwarts house, say Slytherin because of his cunning nature. Then he would have to navigate the politics within the house while also exploring the secrets of the castle. He could also get involved in some kind of mystery that threatens Hogwarts and use his unique skills to help solve it.
He could interact with Harry Potter, Ron Weasley and Hermione Granger. They might be curious about Ciel and his different upbringing.
I'm not sure specifically as there could be many different versions of such a fanfic. But generally, it might involve Ciel's journey to heaven, perhaps his experiences, the people or entities he meets there, and how he copes with this new environment.
Well, it could be that Percy has a hard time adjusting to the wizarding world at first. But then he meets a mentor figure who helps him understand his place in Hogwarts and he starts to thrive. He might even join the Quidditch team and become a star player.
Well, it could be about Naruto arriving at Hogwarts and being confused by all the magic there. Maybe he tries to use his ninja skills in a world full of wizards and witches.
One possibility could be that Harry discovers he has some other magical destiny outside of Hogwarts. Maybe he is taken in by a different group of wizards who teach him their own brand of magic in a hidden location. They might believe Hogwarts is too mainstream or that Harry has a special power that needs to be nurtured away from the school.
Ciel is surely the central figure. However, there could be other characters from the original source material that have also passed on and are in heaven. Additionally, there may be original characters created for the fanfic, such as a special angel who has a particular connection with Ciel. There might also be antagonists in the form of fallen angels or some sort of heavenly bureaucrats who oppose Ciel for some reason.
One possible plot could be Harry dealing with the trauma of living with the Dursleys. He might be constantly bullied by Dudley and neglected by the adults. In therapy, he could start to open up about his feelings of isolation and fear. Maybe he discovers his magic during these therapy sessions as a way to cope, like making small objects move when he gets extremely emotional. This would be a new take on his pre - Hogwarts life, exploring his psychological state rather than just the physical abuse he endures.
The plot might involve Naruto making friends with some of the Hogwarts students. He could show them his unique fighting style, like the Rasengan, and they in turn could teach him some basic spells. For example, Hermione could be intrigued by Naruto's chakra system and Naruto could be amazed by her knowledge of magic. There could also be a conflict where Naruto has to face some dark wizards using his ninja abilities, while also learning how to use magic in a pinch.
Well, it could be about Mal, who might be a new student at Hogwarts. Maybe Mal discovers a hidden magic ability that no one else has. He could make new friends and together they face some sort of mystery in the castle, like a secret room that holds an ancient magic that's in danger of being misused.
In the 'sakura goes to hogwarts fanfiction', it could be that Sakura is a transfer student. She would face the challenges of adapting to the different magical system in Hogwarts. For example, she has to learn about potions and spells in the Hogwarts way. Along the way, she might discover a hidden mystery in Hogwarts that only she, with her special background, can solve. Maybe it has something to do with an ancient artifact that links her world to Hogwarts.