Hermione is often in these fanfictions. She might help Harry understand the more complex magical aspects related to his broomstick. For example, she could research ancient spells that were once used to enhance broomstick speed and try to apply them to Harry's broom.
Draco Malfoy could also appear. In some fanfictions, he might try to steal Harry's broomstick to show off or to gain an advantage in Quidditch. However, in other stories, he could end up teaming with Harry when they both realize that there are greater threats that require their combined skills and the power of Harry's broomstick to face.
Obviously, Harry Potter himself is a common character. He is the main protagonist in the original series and often the central figure in fanfictions related to the broomstick as well. Hermione Granger and Ron Weasley also frequently appear, as they are Harry's closest friends and are usually involved in his adventures.
Hermione is often a common character. In these fanfictions, she might play a different role. For example, she could be the one to discover Harry's unique upbringing and help him understand how it makes him different from other wizards. Ron could also be there, and his friendship with Harry might develop in new ways. Maybe he's a bit more in awe of Harry's magic since he was raised by more powerful magic sources.
Hermione is often a common character. Since she is Harry's closest friend, she usually plays an important role in helping Harry navigate the past. She might use her vast knowledge of magic and history to figure out why Harry was summoned and what they need to do next.
Hermione is often a key character. She might stand by Harry's side, using her intelligence and loyalty to help him through the tough times. She could be the one to encourage him to keep going and not let the disownment break him.
A previously unknown family member could be an important character. For example, an older cousin or an aunt who has been in hiding due to some dark secret related to the family's heritage. They could appear and help Harry navigate the complex world of his family's past, teaching him things that his parents were unable to before their untimely deaths.
Voldemort is often a key character. Since Harry is going dark, Voldemort might play a role in either guiding him into darkness or being an antagonist to his newfound dark power. Another common character is Hermione. She might try to save Harry from the dark path he's on, leading to a lot of conflict between them.
Hermione and Ron are usually quite common. Since they are Harry's best friends, they would be involved in the story when Harry's parents return. They might be curious about his parents, and also help Harry and his parents adjust to the current situation.
The dragon, of course, is a major character. It could be named something unique like 'Fyrstorm'. There might also be Hermione and Ron. Hermione would probably be worried about the legality and danger of raising a dragon, while Ron might be both scared and a bit excited about it.
Hermione would surely be involved. She could be Harry's research partner, helping him find relevant medical information in books and scrolls. Her intelligence and thirst for knowledge would be very useful in exploring new areas of medical magic. Another character could be Madam Pomfrey. She could be Harry's mentor, teaching him the basics of wizarding medicine and guiding him in his new role as a medic.
Harry Potter himself is often a great character in these fanfics. His natural talent on a broomstick can be explored further, like in a fanfic where he discovers new tricks on his Firebolt. Ron Weasley can also be interesting as he sometimes struggles with confidence on a broom, and a fanfic could show his growth in this area.