In this fanfiction, Percy could bring a whole new dynamic to the Twilight universe. His knowledge of the gods and monsters could make him suspect that there's something more to the Cullens than just being vampires. He might start investigating them on his own, which could put him in danger. At the same time, his relationship with Bella would be complex. He would have to balance his role as her brother with his own adventures in the world of demigods.
One way the storyline could be is that Percy uses his demigod powers to protect Bella from the various threats in Forks. For example, he could sense the presence of vampires and werewolves before Bella does and keep her out of harm's way. He might also introduce her to the world of Greek mythology, which would be a huge contrast to the world of Twilight she already knows.
Percy's relationship with Jacob could also be a key part of the story. They might initially be at odds because Jacob is a werewolf and Percy is used to dealing with different kinds of 'creatures'. But over time, they could learn to work together, especially if they both have Bella's best interests at heart. Percy's interactions with Bella herself would be a mix of brotherly love and trying to keep her out of supernatural trouble.
Yes, there are some out there. You can start by looking on popular fanfiction websites like Archive of Our Own. Just search for 'Percy Jackson and Bella Swan' and you'll likely find a variety of stories. However, the quality can vary greatly.
One possible plot could be that Percy somehow ends up in the Twilight world. He meets Bella and they initially clash because of their different personalities and backgrounds. But as they face common threats, like a new type of monster that combines the elements of Greek mythology and the Twilight creatures, they start to fall in love.
Well, in fanfiction, anything can be made possible. One way could be through some sort of magical or divine intervention. Maybe there's a god or goddess who manipulates fate so that Bella Swan and Percy Jackson are siblings. It could also be that their parents have some sort of hidden connection that was never revealed in the original stories. Another idea is that they exist in a different dimension where the rules of their respective universes are merged, allowing for such a relationship to occur.
They could go on a quest to find a magical object that has the power to balance the magic in both their worlds. Since Percy is used to dealing with Greek mythology - related quests and Bella has her own experiences in the Twilight world, they could combine their skills. For example, Percy's ability to fight monsters and Bella's immunity to some vampire powers could come in handy.
Well, one possibility could be that Percy discovers his connection to Nyx and has to deal with the powers and responsibilities that come with it. Maybe he has to face some ancient enemies of Nyx who are now after him because of their relation.
It would be really complex. Their parents would have to deal with two very different children. One is a demigod with powers and a connection to the Greek gods, and the other is a girl involved in the vampire - werewolf drama. There would be a lot of secrecy in the family, trying to hide Percy's demigod world from Bella's friends and vice versa.
Well, Percy comes from a world of Greek gods and monsters, while Bella is in the world of vampires and werewolves. If they were twins, their worlds would collide in a really chaotic way. Percy's demigod powers might be a shock to the Twilight characters. And Bella's knowledge of the supernatural in her world could also surprise Percy's friends. Maybe they'd end up having to fight common enemies that cross over from both their universes.
Well, sometimes in fanfiction, his brother might be a mortal who discovers his demigod heritage later. This could add an interesting twist to the story as he has to adapt to the world of gods and monsters. Or it could be a long - lost half - brother from a different camp, like a son of Poseidon from another part of the world who was hidden away for some reason.
A possible way to redeem this kind of storyline is to give it a backstory. Maybe Bella was forced into prostitution due to some dire circumstances. Then, as the story progresses, she could fight against the system that trapped her. By showing her growth and determination, the story could be more acceptable. Also, adding elements of love and friendship that help her out of that situation would be a good approach.