One plot idea could be that Harry, with his wizarding skills, somehow stumbles into the world of the Cullens. Maybe he's on a mission to find a magical artifact that has ended up in their territory. Another could be that there is a threat that endangers both the wizarding world and the Cullens' vampire world, and they have to team up to face it. For example, a dark sorcerer is trying to create a spell that would control vampires and use them for evil deeds.
One common theme is the clash of two different worlds. The magical world of Harry Potter with its wizards, spells, and Hogwarts, and the vampire - centric world of the Cullens. Another theme is often the idea of friendship or alliance forming between the characters of the two universes.
Obviously, Harry Potter himself would be a main character. He is the central figure in the Harry Potter series. Then, from the Cullen family, Edward Cullen would likely be a main character. He is the most prominent of the Cullens in the Twilight series and his abilities and personality would make for an interesting interaction with Harry.
One interesting plot could be a magical duel between Harry Potter and one of the Cullens. Maybe they meet in a special dimension where magic from both universes co - exist. Harry uses his spells like Expelliarmus while the Cullen uses their vampire - related powers.
One popular 'Harry Potter related to Cullens' fanfiction is 'The Crossover Chronicles'. It imagines a world where the magical elements of Harry Potter blend with the vampire lore of the Cullens. Another one could be 'Potter and the Cullen Alliance' which focuses on how the two groups might form an alliance to face a common threat.
He might have conversations with them about their different worlds. For example, he could talk to Carlisle about the ethics of being a vampire compared to the rules in the wizarding world about using magic. He could also bond with Alice over their shared ability to see things others can't. Harry's prophetic dreams and Alice's visions could be a great topic of discussion.
The plot might start with Harry being in a vulnerable situation and the Cullens taking him in. They'd have to figure out how to raise a wizard in their vampire household. Harry could start to show his magical abilities which might be both a wonder and a bit of a problem for the Cullens. He could also make new friends in the vampire community, and together they could face some common enemies.
The Cullens are used to living in secrecy in their own world. Harry, on the other hand, is constantly in the spotlight in the wizarding world. This could create some interesting interactions. For instance, Bella from the Cullens might be in awe of Harry's ability to handle all the attention. And Harry could be intrigued by the Cullens' calm and collected nature, which comes from their long - lived experiences. They could also clash because of their different moral codes. The Cullens have their own set of rules about not harming humans, while in the wizarding world, there are different rules about dealing with dark wizards and creatures.
One plot idea could be that the Cullens somehow end up in the wizarding world of Harry Potter. Maybe they are mistaken for a new type of magical creature at Hogwarts. Another could be that Harry Potter discovers the existence of the Cullens while on a mission outside the wizarding world and they have to team up to fight a common enemy, like a powerful dark wizard who also has an interest in vampires.
If the Cullens read Twilight fanfic, they might be either amused or appalled. Some fanfic might depict them in ways that are completely different from how they see themselves. For example, they could find some overly romanticized or out - of - character versions of themselves.