Dumbledore could also be a major character. As the headmaster of Hogwarts, he has a big influence on Harry's life at the school. And maybe some of the Hogwarts ghosts like Nearly Headless Nick would play significant roles in the story as well.
The other teachers at Hogwarts, such as Professor McGonagall, Snape (even if his relationship with Harry is complex), and Hagrid could be main characters. They all have their own relationships with Harry and would be part of his life while he lives at Hogwarts.
Since it's about Harry as a mediwizard at Hogwarts, Harry is the central character for sure. In addition, I would expect to see characters like Neville, who could be someone Harry helps as a mediwizard. And then there could be some new characters created specifically for this fanfiction, perhaps other mediwizards in training with Harry or patients with really strange magical conditions that he has to deal with.
Harry is the central figure. But there could be new characters introduced as students or staff. For example, the children of the original characters could be main characters in their own right. Ginny Weasley, Harry's wife, might also be prominently featured, perhaps as the Quidditch coach or in charge of some other aspect of school life. Additionally, old professors like McGonagall could still be around and be important characters.
Obviously, Harry Potter is one of the main characters. He is the boy who lived and has his own story filled with battles against Voldemort. Nicolas Flamel is another main character. He is an ancient and very powerful alchemist who created the Philosopher's Stone.
Obviously, Harry Potter is one of the main characters. He is the one who is living with the Greengrass family.
It could also include some new characters created specifically for the fanfiction. Maybe a young wizard or witch from a minor house who plays a crucial role in uniting Hogwarts. They could have some special abilities or a unique backstory that helps in bringing the students together.
The heir themselves would be a main character, of course. And Harry Potter might still play a role, either as a friend or a rival to the heir. Dumbledore could also be a major character, guiding or observing the heir's journey.
Other main characters could include the ward's new friends at Hogwarts. They could be from different houses and have different personalities. Together, they form a group that helps the ward through various adventures, whether it's exploring the Forbidden Forest or uncovering secrets within the castle walls.
Most likely, the Hogwarts Four would consist of Harry Potter, who is known for his courage and his connection to Voldemort. Hermione Granger, with her vast knowledge of magic and quick thinking. Ron Weasley, who brings loyalty and a sense of humor to the group. And it could be Luna Lovegood as the fourth member. Luna has her own unique perspective on the wizarding world and could add a different flavor to their adventures.
Obviously, Harry Potter is the main character. He is the one taking on the role of the guardian. Hermione and Ron usually play important supporting roles as well. They help Harry in his mission to protect Hogwarts with their knowledge and skills.
Their children could also be important characters in this fanfiction. Depending on how the author writes it, their kids might inherit some of their parents' special abilities or have their own unique powers. And they could be involved in various adventures or family situations.