Obviously, Harry Potter would be one of the main characters. Since it's about him saving the Flamels. The Flamels themselves, Nicolas and Perenelle, would also be main characters as they are the ones being saved.
Well, it could be that the Flamels are in danger due to Voldemort's return. Harry Potter, being the hero, steps in. He might enlist the help of his friends like Ron and Hermione. They could go on a quest to find a powerful magical artifact that can safeguard the Flamels. Harry's knowledge of the wizarding world and his past experiences fighting evil would be crucial in this story.
Obviously, Harry is one of the main characters. And the Flamels, who are very important in the wizarding world. They are known for creating the Philosopher's Stone.
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 and the Jedi would be the main characters. Maybe Luke Skywalker and Harry could form an alliance.
The main characters are Dudley and Harry. Dudley, who has usually been portrayed as a bully in the original series, is now the hero. Harry, on the other hand, is the target of whatever danger is present in the fanfiction. There might also be other supporting characters like Dudley's parents or some of Harry's friends from Hogwarts who could play a role in the story.
One could be an American wizard named Jack. He could be a powerful spell - caster from a prominent American wizarding family. Maybe he's an expert in elemental magic, which is more developed in the American wizarding community. Another could be a witch named Lily (not related to Harry Potter's mother). She could be a healer who has knowledge of unique herbs and potions found only in America. And there could be a young American wizard named Max who is really good at magical inventions. He could create devices that help in the fight against the dark forces in the Harry Potter world.
It could be a dark wizard who has his eyes on Cintra's powerful magical artifacts. He wants to use them to gain more power and is willing to destroy Cintra to get them.
In some fanfictions, an ancient evil entity that has been awakened might be the main antagonist. This entity could be after Ginny because she has some special power or connection that the entity wants to use for its own dark purposes. And of course, there could be a jealous wizard who wants to get rid of Ginny to have Harry all to himself.
It could be a rogue Death Eater who has escaped from Azkaban. This Death Eater might be desperate to regain his power and believes that unicorn blood will give him the strength he needs. So he sets out to capture a unicorn in the Forbidden Forest, which is where Harry comes in to stop him.
It could be Death Eaters who have a new plan. They might want to create chaos in the Muggle world by targeting the Queen. They see her as a symbol of Muggle power and order, so by attacking her, they hope to disrupt the Muggle - wizard relationship.