One popular HP crossover fanfiction is the one where Harry Potter crosses over with the world of Middle - earth from 'The Lord of the Rings'. In this type of story, you might see Harry and his friends facing the challenges of Sauron along with the magical threats in their own world. Another could be a crossover with the 'Percy Jackson' series, where the demigods and wizards interact in interesting ways. For example, they might have to combine their powers to fight a common enemy that threatens both the wizarding world and the world of the Greek gods.
Another theme is the idea of different cultures coming together. The characters from Sunnydale have a very different upbringing and set of values compared to those in the wizarding world. This can lead to some interesting character dynamics, like Hermione trying to understand Buffy's more street - smart ways or Xander being in awe of the magical grandeur of Hogwarts.
A common theme is the clash of different powers. The magic from Harry Potter and the superpowers of the Avengers often collide and combine in interesting ways.
Imagine a story where the Deathly Hallows are in the Teen Wolf world. The Teen Wolf characters don't understand what they are at first. But then they team up with some HP characters who have come to retrieve them. They have to battle a powerful dark force that wants to use the Hallows for evil in the Teen Wolf realm. This would combine the magical elements of HP with the action - packed werewolf lore of Teen Wolf.
One common theme is the clash of different power systems. In both The Vampire Diaries (TVD) and Harry Potter (HP), there are unique forms of power. In crossovers, it's interesting to see how the magic of HP and the supernatural abilities in TVD interact. For example, how would a vampire react to a Patronus charm? Another theme is the exploration of different cultures. The wizarding culture in HP and the vampire - werewolf - witch culture in TVD are very different, and crossovers often explore how characters from one world adapt to the other.
One interesting HP KHR crossover fanfiction could be where the characters from 'Harry Potter' find themselves in the world of 'Katekyo Hitman Reborn!'. For example, Harry Potter might end up at Namimori Middle School and interact with Tsuna and his friends. They could learn about each other's magic systems, like how the magic in 'Harry Potter' is more traditional with wands and spells, while in 'KHR' it's more about the Dying Will Flame. Another story could involve the Death Eaters somehow getting involved with the Mafia in 'KHR' and causing chaos across both worlds.
Begin by choosing the HP crossover concept. If it's an HP and 'Game of Thrones' crossover, consider the political intrigue in both worlds. In HP, there's the politics within the Ministry of Magic, and in 'Game of Thrones', there are the power struggles for the Iron Throne. Think about how the characters from both will interact. Maybe Dumbledore could be like a wise maester in the 'Game of Thrones' world. Once you have these ideas in place, start writing the opening scene. It could be a dramatic event that brings the two worlds together, like a dragon from 'Game of Thrones' showing up at Hogwarts.
One interesting story could be where the magical world of Harry Potter intersects with the vampire - werewolf lore of Twilight in Hogwarts. Maybe a Twilight character ends up at Hogwarts as an exchange student and has to navigate the magical classes and the politics within the school, all while hiding their true nature as a vampire or werewolf.
You can start by looking on fanfiction.net. It has a large collection of various fanfictions, including 'hoo hp crossover' ones. Just use the search bar and type in relevant keywords to find what you're looking for.
There's a fanfic called 'Percy Jackson in the Wizarding World'. In this story, Percy finds himself accidentally transported to Hogwarts. His skills as a demigod are put to the test in the magical school, and he has to navigate the complex relationships and rules there. It's full of action and humor.