There are quite a few great ones. Some focus on the unique challenges of their relationship, like how Bella copes with Edward's vampiric nature while being human. For example, 'A Different Kind of Love' shows their relationship evolving in a very heart - warming way.
One interesting aspect could be how their relationship dynamics change. In the original, Edward was the vampire and Bella was the human, so reversing their roles might lead to a different power dynamic. For example, Bella as a vampire would have more physical strength and speed, which could make her more protective of Edward. Also, Edward as a human might struggle with his mortality compared to Bella's immortality, creating new tensions and storylines in the fanfiction.
The popularity comes from the fact that fans love the Twilight couple. Fanfic allows them to explore more of Bella and Edward's relationship. It can add new elements not in the original books.
Another good one is 'The Vampire's Mate'. It delves deeper into the vampire lore and how Bella, as a human, fits into their world. The relationship between Edward and Bella is portrayed in a more intense and detailed way, which makes for a very engaging read.
I'm not sure if there is such a specific fanfic. There are countless fanfics out there, and while the 'Twilight' series has a large fanfic community, this particular combination seems rather unorthodox. It might exist in the vast realm of fan - created works, but it's not a common or widely - known trope within the official 'Twilight' lore.
One common theme is the exploration of power dynamics. Since Bella is a vampire and Edward is human, it changes the traditional power balance in their relationship. For example, Bella may have to protect Edward from other vampires.
Some fanfics might involve alternate universes where Bella is a human but has some special power that attracts Edward. For example, she could have the ability to see the future, and this changes the dynamic of their relationship. It could also be a story where Edward struggles more with his vampire nature while being with Bella, adding more drama to the plot.
Love against all odds is a very common theme. Since they are from different species, there are a lot of obstacles in their relationship. For example, in many fanfictions, Bella has to control her vampire instincts around Edward, which adds a layer of tension.
The main characters are Edward, who is a vampire, and Bella, who is a human. Edward is often depicted as mysterious, brooding, and having a strong sense of protection towards Bella.
Another common theme is the struggle between the vampire and human worlds. There are often conflicts arising from the differences in their natures, values, and lifestyles. Fanfiction writers usually show how Edward and Bella deal with these differences and try to find a balance between the two worlds.