Well, the answer might actually be Willow from Buffy. In later seasons, Willow becomes extremely powerful with her magic. She can do things like reshape reality and has a vast knowledge of magic spells. In a crossover, her magic could potentially overpower many of the vampires in The Vampire Diaries world. Even the originals might have a hard time against her if she's at her full power. But, on the other hand, the vampires in The Vampire Diaries have their own unique abilities that could pose a challenge to Willow as well.
I think Klaus from The Vampire Diaries would also be a very powerful character in a crossover. He's an original vampire - werewolf hybrid with incredible strength and a very cunning mind. But Buffy has the power of the slayer, which gives her enhanced physical abilities and a sort of sixth sense for the supernatural. If they were to face off, Buffy's slayer instincts might give her an edge, but Klaus's raw power and immortality would make it a tough fight.
Perhaps a spell gone wrong in the Buffy universe causes some of the main characters from there to swap bodies with characters from The Vampire Diaries. This could lead to humorous and tense situations as they try to figure out how to reverse the spell while still dealing with the threats in each other's worlds.
One popular theme is the relationship between the characters. In both shows, there are complex love triangles and friendships that fanfiction often explores further. For example, in The Vampire Diaries, the relationship between Elena, Stefan, and Damon is a huge draw for fanfiction writers. Another theme is the battle between good and evil. Buffy's slayer duties and the vampires in The Vampire Diaries provide ample material for stories centered around fighting the forces of darkness. Also, character backstories are often delved into. Writers might create stories about how a character became a vampire or how Buffy got her slayer powers in the first place.
One popular Buffy and Vampire Diaries fanfiction might be those that explore a crossover between the two universes. For example, a story where Buffy Summers meets the Salvatore brothers. It could be interesting to see how their different vampire - slaying and vampire - being concepts interact.
Imagine if Elena Gilbert was somehow connected to an Infinity Stone. This would draw the attention of Thanos, but also the Avengers. The Vampire Diaries characters would have to protect Elena while also dealing with the fact that the Avengers are now in their small town. There could be a lot of mistrust at first, but as they learn more about each other's motives and capabilities, they form an alliance to keep the Infinity Stone out of Thanos' hands.
Tumblr can be another source. There are often fanfiction writers who post snippets or links to their full - length Buffy and Vampire Diaries fanfictions on their blogs. You can search relevant hashtags to discover new and interesting stories.
One great 'Vampire Diaries' crossover fanfiction is 'The Vampire Diaries and Supernatural: The Crossover'. It combines the dark, supernatural elements of both shows really well. The characters from each show interact in a believable way, and the plot keeps you hooked from start to finish.
A popular one is 'A New Alliance'. In this fanfiction, the plot brings together the different supernatural elements from 'The Vampire Diaries' and 'The Originals' in a unique way. The author does a great job of maintaining the personalities of the original characters while also creating new and exciting storylines. It's a must - read for fans of the two shows.
Well, a frequent theme is the clash of different cultures. In a Vampire Diaries and Harry Potter crossover, you have the magical culture of Hogwarts clashing with the vampire - based culture of Mystic Falls. This can lead to misunderstandings and conflicts that drive the story forward. Also, survival is a big theme. In many crossovers, the characters have to find a way to survive in a new and more dangerous world created by the crossover. For instance, in a Vampire Diaries and Buffy the Vampire Slayer crossover, the vampires from Vampire Diaries might have to adapt to the slayer - filled world of Buffy or face being staked.
In The Vampire Diaries, Elena and the Salvatore brothers, Stefan and Damon, are extremely popular. Elena because she is the central female character and her relationships with the two vampire brothers are so complex. Stefan is often written about because of his brooding nature and his struggle with his vampire side. Damon, with his bad - boy charm, is a favorite too. In Buffy, Buffy herself is a very common character in fanfiction. Her role as the slayer and her relationships with her friends like Willow and Xander make her a prime choice. Spike is also very popular, especially his relationship with Buffy which is full of tension and emotion.
One idea could be that the Pretty Little Liars characters find themselves in Mystic Falls. Maybe A is somehow related to the supernatural threats in The Vampire Diaries. The liars could team up with the Salvatore brothers to figure out the mystery behind A while also dealing with vampires and witches.