Obviously, Harry himself is the central character. Then, there could be characters like Dumbledore who might play a role in guiding Harry about his new heritage. Hermione would also likely be involved, using her knowledge to help Harry understand the Pendragon history.
Ron could be another character in the 'harry is the heir of pendragon fanfiction'. He would probably support Harry as he always does. And perhaps some ancient wizard or witch related to the Pendragon line could appear, like an old mentor figure who imparts wisdom about the Pendragon legacy to Harry.
In this fanfiction, there could be antagonists related to the Pendragon history as well. Maybe a dark wizard who wants to stop Harry from fully realizing his Pendragon powers. And other magical creatures that were once associated with the Pendragons might also make an appearance, either as friends or foes of Harry.
There could be other characters from the original Harry Potter series who play important roles. For example, Hermione might be there to help Harry research and understand his Pendragon heritage. Ron could also be by his side, providing support and comic relief in the face of all the new and strange things that come with this discovery.
Hermione is the central character as the heir. Harry and Ron will surely be there, supporting her or getting into some trouble with her. Professors like McGonagall could be involved as well. They might either guide Hermione in her new role or be a bit skeptical at first. There could also be some antagonists, like Malfoy, who might try to undermine Hermione's position as the heir.
The main characters could include the heir's family members from the Pendragon side, even if they are long - dead, they might appear in memories or visions. Dumbledore could also be a main character as he is a very important figure in the Harry Potter world. He might guide the heir, knowing about their special heritage and seeing how it could be beneficial in the fight against evil. Another possible main character could be a villain who wants to use the heir's power for their own dark purposes.
Obviously, Harry Potter himself would be the main character. Hermione and Ron would also be important as they are Harry's closest friends and would be involved in his journey as the heir.
Perhaps in the 'harry is the heir of pendragon fanfiction', Harry's new status as the heir of Pendragon causes a stir in the wizarding world. Some might fear his new - found power, while others might see him as a great hope. He could be drawn into a political struggle within the magical community as a result.
Neville could be involved too. He has grown into a strong wizard and would surely want to help his friend. Ginny, who has a special connection with Harry, would be at his side constantly. There could also be some new characters introduced, like a healer from a far - away land who has unique knowledge about Harry's condition.
Dumbledore could also play a role. He might see Harry's weight loss journey as part of his overall growth and offer some cryptic yet inspiring words. Maybe he arranges for Harry to have special training sessions with the ghosts of Hogwarts, who have unique ways of making exercise fun. And of course, the Hogwarts professors like Madam Pomfrey could be involved, ensuring Harry's health during his weight loss process.
Obviously, Harry Potter himself is the central character. Hermione Granger and Ron Weasley are also very likely to be involved. They might try to help Harry regain his hope. Dumbledore, even if he's dead in the original story, could appear in flashbacks or as a guiding spirit, trying to inspire Harry. Snape could also be part of it, as his complex relationship with Harry could add more depth to the story of Harry losing hope.
One interesting plotline could be the discovery of the connection between being the heir of Pendragon and Harry's existing powers in the wizarding world. Maybe it gives him new abilities or a different perspective on magic.
Obviously, Harry Potter himself is the central character as the one being abused and neglected. The Dursleys are also key characters as they are the ones who abuse and neglect him in the original story. Hermione and Ron might also be involved as they could be the ones to discover Harry's situation and try to help him. Dumbledore could also be a part of it, perhaps as someone who failed to notice or prevent Harry's abuse initially.