The plot could potentially revolve around Merlin seeing something special in Harry Potter. As Merlin is from the time of the founders, he might have his own reasons for getting involved. He could introduce Harry to the magical world in a completely different way than Hogwarts did. For example, instead of the traditional Hogwarts curriculum, Harry might learn more about the origins of magic, how the founders built Hogwarts, and Merlin could also share his own experiences and wisdom with Harry, which would give Harry an edge in his fight against the Dark Arts and Voldemort.
Obviously, the main characters would be Merlin, Harry Potter, and probably the founders would be mentioned or play some role in the background. After all, Merlin is from their era.
Well, clearly Merlin and Harry Potter are the main characters. Merlin, with his powerful magic and wisdom from a different era, and Harry, the boy - who - lived from the modern wizarding world.
One interesting plot could be Merlin using his ancient magic to protect Harry from the Dursleys in a more magical and direct way than in the original story. Maybe he creates a magical shield around the house that only allows good magic in and keeps out any harm intended for Harry.
There could be. Fanfic writers often come up with unique concepts. The founders' trains might be used to transport students in a time long before the Hogwarts Express we know. It could be a way to show a different side of the founders' era, with different magical technologies or traditions associated with these trains.
Well, it could be about the founders coming back to Hogwarts to fix some long - standing issues. Maybe they return to deal with the dark magic that has seeped into the school over the centuries.
It could be a symbol of the founders' era. Maybe it represents the early magic and technology of Hogwarts. For example, it could be a more primitive form of the Hogwarts Express but with unique magical properties specific to the founders' time.
It could be Harry Potter himself. Since he has so many special qualities and a deep connection to Hogwarts, he might be revealed as an heir. Maybe he has some latent powers related to one of the founders that haven't been discovered yet.
In addition to the trio, there could be characters like Professor McGonagall. She would surely notice the changes in Harry and might try to guide him. Also, the ghosts of the founders themselves could be considered main characters in a sense. Since Harry is possessed by them, they would have a significant influence on the story, perhaps communicating with Harry or causing events to unfold around him.
Obviously, the four founders - Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw, and Salazar Slytherin would be main characters as they are the ones returning.