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 aspect could be the unique relationship between Klaus and Kol that is explored. In fanfiction, it might delve deeper into their brotherly bond, perhaps showing how they support or clash with each other in different scenarios that the original work didn't fully explore.
You can try some popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of various fanfictions, and there's a good chance you'll find 'klaus and kol lemon fanfiction' there.
There's also 'A Hybrid's Adventure in Hogwarts'. In this fanfiction, the hybrids from TVD end up in the world of Harry Potter. It's full of action and adventure as they navigate through the wizarding school, dealing with spells and potions while also having their own unique vampire - werewolf powers. It's a fun read if you like crossovers.
One idea could be that Kol and Elena are in a forbidden love situation. Maybe in a world where the supernatural factions are at odds, and their relationship is seen as a threat to the balance. Another could be a time - travel plot where Elena goes back in time and meets a younger Kol, changing the course of their relationship.
The fact that they come from different 'eras' in the vampire world could also be a problem. Kol has been around for a very long time and has different values and beliefs compared to Elena. This could lead to misunderstandings and arguments as they try to navigate their relationship.
One popular plot is Kol's redemption. He tries to atone for his past misdeeds in the vampire world. This could involve helping humans or making amends with his family in ways that the show didn't explore. For instance, he might protect a small town from other evil vampires to prove he can be good.
The possibilities are endless. It could be a story about her trying to find her place in the supernatural world, or it could be a time-travel adventure. Maybe it even reimagines certain events from the TV show from her perspective.