The central character is the apprentice. In addition to that, there could be a group of characters that form a sort of council within Hogwarts, made up of professors and older students, who are skeptical about the apprentice's new - found knowledge of the founders. On the other hand, there may be a small group of friends that the apprentice makes, who are loyal and support the apprentice through all the challenges. These friends could come from different backgrounds and houses, adding to the diversity of the story.
The apprentice is obviously one of the main characters. They are likely to be a young wizard or witch with great potential. Then there might be characters representing the different houses of Hogwarts, like a descendant of Gryffindor who is a mentor to the apprentice. There could also be a rival apprentice who has different ideas about the founders' magic.
Often, the main characters would be the heirs themselves. There could be a character who is the heir of Gryffindor, perhaps a young student who has always shown great courage and a sense of justice. Another main character might be the heir of Slytherin, who at first seems a bit of an outcast because of the negative reputation of Slytherin but turns out to have a complex and important role.
Obviously, the four founders - Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw and Salazar Slytherin are main characters as they are being reborn. They bring their unique personalities and magical abilities back to the story.
The main characters would surely include Harry Potter. Since it's about him meeting the founders, he's central to the story. As for the founders, they are key too. Godric Gryffindor might be the most enthusiastic about meeting Harry, seeing in him the true spirit of Gryffindor. Helga Hufflepuff could be the nurturing one, teaching Harry about the importance of hard work and loyalty. Rowena Ravenclaw might offer him wisdom, and Salazar Slytherin could present a more complex relationship, as his views on blood purity might clash with Harry's, but still be an important part of the story as Harry tries to understand and reconcile different magical ideologies.
You'll usually find characters like Godric Gryffindor, Salazar Slytherin, Rowena Ravenclaw, and Helga Hufflepuff. They might be present in spirit or through memories stored in the staff. And then there are the modern - day students who stumble upon the secrets of the staff. They could be original characters created by the fanfiction writer or minor characters from the original books who are given more depth in these stories.
Well, perhaps a plotline where the apprentice has to deal with the different personalities of the founders' legacies. There could be a conflict between the Gryffindor - like boldness and the Slytherin - like cunning within the Hogwarts community that the apprentice has to navigate. It might also involve the apprentice trying to bring back an old tradition that was forgotten but was crucial to the founders' vision of the school.
Obviously, Harry Potter would be one of the main characters. And Naga Sadow, as the one Harry is apprenticed to. There might also be some of Harry's friends from Hogwarts like Hermione and Ron, who could be trying to bring him back from the dark path he's on.
Another possible main character could be a new villain. Since Harry is in a new role as an apprentice, there could be someone who wants to steal the secrets of Ollivander's wand - making. This villain could be a dark wizard or a rogue wizard who has his own motives for wanting to control the wand - making process. Harry would then have to protect Ollivander and the shop from this threat.
Neville Longbottom is another possible heir. He has a strong connection to Gryffindor through his family's long - standing association with the house. His growth from a shy and clumsy boy to a brave and powerful wizard could be part of a story where he is the heir of the founders. His ability to stand up to the Death Eaters in the final battle shows his hidden strength, which could be related to the founders' magic.
Helga Hufflepuff is often quite popular. She represents kindness and loyalty, and in fanfiction, she might be portrayed as the one who keeps the founders together during their disagreements. Her character can be explored more deeply, like her backstory and how she came to value hard work and fairness so much.
Sometimes, the magical creatures that were around during the Founders' time can be popular characters in these fanfictions. For example, a phoenix that was a companion to one of the Founders and played a significant role in a particular event. They bring a touch of magic and mystery to the story and can be really engaging for readers.