There could also be some new characters introduced. Maybe a student who also had a late start in a previous year and can give Harry some advice. Or a magical creature that Harry encounters on his way to Hogwarts late and that creature becomes some sort of guide or protector for him during his time at Hogwarts.
One possibility is that Harry's late arrival at Hogwarts could change the dynamics of the relationships he forms. For instance, instead of being in the same boat as the first - years from the start, he might end up befriending some older students who take him under their wing. Also, his late start could mean that he discovers parts of Hogwarts that others haven't yet, like secret passages or rooms that are only accessible to those who arrive late or are in a certain situation.
His family members also play roles. His father, Harry Potter, could be mentioned, perhaps giving Albus advice or being a source of inspiration. His siblings might also be included, adding family - related sub - plots to the story.
Hermione Granger would likely be a main character. She could use her vast knowledge to help Harry in his efforts to fix Hogwarts, whether it's researching ancient spells for repairs or coming up with new educational strategies.
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.
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.
Obviously, Harry Potter himself. Then there would be his friends like Hermione and Ron. They could be his advisors or teachers at Hogwarts. Dumbledore might also make an appearance in the form of a memory or a portrait that gives Harry guidance. And of course, the students of Hogwarts would be important characters too.
Harry Potter himself is also very popular. He could be seen as an older, wiser apprentice passing on his knowledge of fighting dark magic to the new generation of students. His adventures against Voldemort give him a lot of experience to share.
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.
Draco Malfoy is often a popular character in these fanfictions. After Hogwarts, he might be trying to redeem himself, or there could be a love story between him and a character like Hermione. His complex past and family history make for interesting storylines. Another popular character could be Neville Longbottom. He has grown so much during his time at Hogwarts, and in fanfiction, he could be a great teacher at Hogwarts, passing on his knowledge of Herbology and his courage to the new students.