It might be an ancient magical being that has the form of a queen. She could have ties to the very origins of magic in the Harry Potter universe and decides to save Harry because she foresees his importance in the future of magic. For example, she could be a guardian of some sort of magic that is crucial for Harry to defeat Voldemort in the long run.
It could be an original character created specifically for the fanfiction. A young and beautiful queen of a small, yet prosperous kingdom, who has a strong will and a love for her people. She might be open - minded and curious about the wizarding world, which makes her a perfect match for Harry.
It could be the Queen of England, as in the real - world monarchy. In the fanfiction, she might be a figure with hidden knowledge of the wizarding world and decides to use her power to rescue Harry.
Well, it might be that Harry Potter is accidentally transported to a non - magical realm where he is in trouble because he doesn't understand the Muggle world completely. The Queen, who has some knowledge of magic or is in contact with a secret magical society, discovers Harry and saves him from the perils of this strange new world for him.
Maybe it's a university student who is majoring in music and is doing a project on Queen. She's at a local pub where there's an open - mic night and Harry, who is there to experience Muggle culture, hears her talking passionately about Queen. He's immediately attracted to her passion and they start to get to know each other, leading to their engagement later.
Well, it could be that the Queen has a special connection to the wizarding world in this fanfiction. Perhaps she has been secretly informed of Harry's bravery and selflessness all along. And as a symbol of the British monarchy, she knights him to show that the Muggle and wizarding worlds can have a positive relationship. So, she bestows this honor on Harry.
There could be some of Harry's friends who might play a role. They could be the ones who encourage Harry to meet the Queen or who give him advice on how to behave in front of her.
Obviously, the Queen would be one of the main characters. And Harry Potter himself would probably be in it too, since it's a Harry Potter fanfiction.
It could be a dark wizard who wants to disrupt the new relationship between the wizarding world and the queen. This wizard might see Harry's position as a threat to his own plans of taking over the Muggle world starting from the monarchy.
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.
Obviously, the Queen of England would be one of the main characters. Harry Potter himself would also be a key character as he is the central figure in the Harry Potter universe. Maybe Hermione could also be involved as she is very intelligent and could help the Queen understand the wizarding world better.