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.
Another plot could be about a love triangle between Harry Potter, a wizard from Hogwarts, and a member of the Cullen family. This would be a complex relationship as they come from different worlds with different values. The wizarding world's rules about love and relationships would clash with the more modern - day concepts in the Cullen's world, creating a lot of drama and tension.
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.
One interesting plot could be that they are distant relatives through some ancient wizarding bloodline. Maybe there was a curse placed on the family long ago that led to their enmity.
In some Harry Potter fanfictions, there might be plots where characters use magic to create unique money - making schemes. For example, a character could use a spell to multiply rare magical items and then sell them at a profit in Diagon Alley. Another idea could be a wizard starting a business teaching other wizards about Muggle finances, which is a new concept in the wizarding world.
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.
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.
One interesting 'Harry Potter Cousin Cullens' fanfiction could be the one where the magical world of Harry Potter collides with the vampire - filled world of the Cullens in a way that Harry discovers he has a long - lost cousin among the Cullens. This could lead to a whole new adventure where he has to deal with the vampire side of his family while still being part of the wizarding world.
A really cool plot could be that they turn into humans and then try to blend into high school as normal students. They have to deal with typical high - school drama like fitting in, making friends, and dealing with bullies, all while hiding their true identities from everyone around them.
One interesting plot could be Bella developing a new power while living with the Cullens. For example, she might gain the ability to communicate with animals like some of the other vampires. This would add a new dynamic to her relationship with the Cullens and also pose new challenges and adventures as they try to keep it a secret from the outside world.
In some Harry Potter 8 fanfictions, there are plots where the characters continue to face new dark magic threats. For example, a new dark wizard might emerge, and Harry, Hermione and Ron have to use their combined skills and knowledge to defeat this new foe. Another plot could be about the exploration of the wizarding world's past in more depth, revealing secrets that were previously unknown.
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.