There could also be other characters from the Harry Potter universe like Hermione and Ron. They might be involved in helping Harry navigate this new world of being connected to the Charmed Ones. And from the Charmed side, there could be Leo, their Whitelighter, who might have some interesting interactions with the magical folk from Harry's world.
Harry Potter is the central figure. Then, the 'charmed one' which could be a previously unknown character or a new take on an existing character from the Harry Potter universe. There might also be antagonists. Maybe some dark wizards who want to use Harry's connection to the charmed one for their evil purposes. And of course, Dumbledore or other Hogwarts professors might play important roles as they often do in stories related to Harry, guiding him and helping him understand his new situation.
Often, in such fanfiction, new original characters are introduced. They could be the ones who created the charmed lemon in the first place. But it's also possible that characters like Dumbledore could play a significant role. He might know more about the charmed lemon than he lets on and be guiding the other characters from behind the scenes. Neville could also be a main character, using his skills with plants to take care of the charmed lemon or study it.
Definitely characters from both 'Charmed' and 'Harry Potter'. From 'Harry Potter', Harry, Hermione, and Ron are very likely to be main characters as they are the central figures in the original series. In 'Charmed', the Halliwell sisters, Prue, Piper, and Phoebe, would be prime candidates. Their different powers and personalities would create interesting dynamics when interacting with the 'Harry Potter' characters.
Harry Potter is a given. In addition to him, I think there could be other characters from the Harry Potter series who might also make an appearance. From the Charmed side, apart from the Halliwell sisters, characters like Leo Wyatt could be important. Since it's a fanfiction that combines two universes, it might also introduce new characters that are created specifically for this story to bridge the gap between the two worlds. For example, a character who has knowledge of both the magic in the Harry Potter world and the power of the Charmed ones.
Hermione is often a popular crossover character. Her intelligence and magical knowledge make her a great fit in the Charmed universe. She can easily adapt to new magical situations and offer her unique perspective.
It could be about a story where Harry Potter is the son of a person who is charmed in some way. Maybe this 'charmed one' has some special powers or a unique background that influences Harry's life in the fanfiction world. It might explore new adventures, relationships, or powers that Harry has because of his connection to this 'charmed one'.
Obviously, the Dark One is a main character. Harry Potter himself also often plays a crucial role as he is usually the one who has to face the Dark One in some way.
One key element could be how Harry's 'charmed' status affects his relationships. For example, it might change how his friends view him or interact with him. Another element could be his newfound abilities or powers that come with being 'charmed'. It might also explore how the wizarding world as a whole reacts to Harry having this special status.
There could be a really interesting fanfiction where the magical worlds of Charmed and Harry Potter collide with Harry and Maggie. Maybe they team up to fight a new kind of dark magic that threatens both their realms. They could each bring their unique magical abilities to the table. Harry with his wizardry from Hogwarts and Maggie with her powers as a Charmed one.
Obviously, Harry Potter himself could be a main character. He could interact with the members of One Direction, like Niall Horan. Maybe Niall is a new student at Hogwarts and Harry is assigned to show him around.