There could also be a new character introduced as the main character. Maybe someone who discovers Merlin's return and has a special connection to him. This character could be on a journey to understand Merlin's purpose in returning and ends up being the focus of the story as they interact with both Merlin and the existing Harry Potter characters.
Harry Potter might still be the main character even with Merlin's return. Merlin could be more of a guiding or helping figure, and Harry would be the one who ultimately has to face the main challenges with Merlin's assistance. So Harry would remain at the core of the story.
It could be a new student at Hogwarts. A young witch or wizard who discovers they have the Eyes of Merlin and has to deal with the sudden power and the attention it brings from both good and bad forces.
The 'return of Merlin' in Harry Potter fanfiction could be a really exciting plot. It might be that Merlin has been trapped or in some sort of stasis for a long time. His return would stir things up. He could be the key to solving some of the most difficult problems in the wizarding world, like the mystery behind certain dark artifacts or the origin of some powerful curses. He could also form alliances with the existing characters, creating new and interesting relationships.
It might be a new transfer student from a far - off magical school. This student brings with them the knowledge or potential to be the new Merlin figure. They could have a different approach to magic compared to what's taught at Hogwarts, which makes them stand out as a possible Merlin - like character.
Another option could be Luna Lovegood. She has a very unique perspective on magic already. If she were Merlin's apprentice, she could bring her eccentric ideas and combine them with Merlin's ancient magic. Her friendship with Harry Potter and the others could also play a big role in how she uses her newfound status as Merlin's apprentice to help the wizarding world.
It's hard to say without reading it, but it could be the main characters from the Harry Potter series like Harry, Hermione, and Ron. They might be the ones exploring Merlin's legacy.
Merlin would be the central figure. Ron Weasley could play an important role too. He might be a bit skeptical of Merlin at first but then come to respect him. Dumbledore could also be a major character, having some sort of connection or prior knowledge about Merlin's return.
Often, there are other characters from the original Harry Potter series as well. For example, some fanfictions might include Hermione as a friend or mentor to the descendant. She can use her intelligence to help the main character understand their powers better. And of course, there could be some original characters created specifically for the fanfiction, like a mysterious wizard who also has a connection to Merlin's past.
Obviously, Merlin is the central character. His character is the focus as he returns and the story usually revolves around his actions, decisions, and how he impacts the world around him again.
Yes, there are likely some fanfictions out there with this concept. The idea of Merlin reincarnating as Harry Potter combines two very popular magical universes. It allows for a lot of interesting plot twists and character development. Writers might explore how Merlin's ancient magic and knowledge would manifest in the modern world of Harry Potter, and how it could change the course of the story we know.
In 'Harry Potter Return of the Black Family' fanfiction, Hermione Granger can also be a main character. Her intelligence and knowledge of magic could be crucial in helping the Black family deal with their various issues. Ron Weasley might also be there, providing his loyalty and friendship. Additionally, characters like Draco Malfoy could have a role to play, as his family is related to the Blacks through marriage, and his own journey of change or alignment with the Black family's new direction could be explored.