Maybe Edward joins the Volturi to gain more power. He might see it as a way to protect Bella in a different, more forceful way. The Volturi are very powerful, and he could learn new skills or gain access to resources that would help him keep Bella safe from other threats in the vampire world.
In this fanfiction, it could be that Edward joins the Volturi because he's disillusioned with the Cullen way of life. The Volturi have a strict and ordered existence, and perhaps he's attracted to their sense of purpose. He may believe that by joining them, he can bring about some positive change within the Volturi, like making their rules more humane, although that would be a big challenge given their long - held traditions.
It could be one of the traditional Volturi members who oppose Edward's presence. They might see him as an outsider who could disrupt their long - established order. For example, Caius might be against Edward joining as he's often portrayed as more rigid and less accepting of new vampires in the Volturi.
One possibility is that Bella is forced to join the Volturi for some reason. Perhaps the Cullens are in trouble and the Volturi offer Bella a deal - join them and they'll spare the Cullens. So she enters their world, where she has to deal with the different personalities among the Volturi members, like Aro's calculating nature and Caius' harshness.
In this fanfiction, she might gain new powers. Since the Volturi Guard is known for its strength and special abilities, Bella could be transformed in many ways.
Well, he might bring chaos. The Volturi are a strict and traditional vampire coven. Percy is a bit of a rebel. He might not like all their rules. But on the other hand, his strength could be an asset. The Volturi could use him to intimidate other vampires. However, Percy might also try to change things in the Volturi. For example, he could try to make them more lenient towards some vampires who are just trying to survive. In the end, it could go either way, either he becomes a valuable member or causes a big split in the Volturi.
One great 'bella joins volturi fanfiction' is 'Bella's New Path' where she discovers new powers within the Volturi. It has an interesting take on her relationships with the Volturi members.
Caius is another important character in such fanfictions. He is usually portrayed as quite strict and unforgiving, and his reactions to Bella joining the Volturi can range from suspicion to begrudging acceptance. Also, Jane, with her special ability, has interactions with Bella that can be both menacing and oddly fascinating.
In this fanfiction, Harry Potter might bake for the Volturi as a peace offering. He could be aware of the Volturi's power and influence in the vampire world and wants to establish a connection. The baked items could hold some magical properties that are beneficial to the Volturi, like cakes that enhance their strength or cookies that give them better control over their vampiric abilities.
Obviously, Bella is one of the main characters. And then there are the Volturi leaders like Aro, Caius, and Marcus. They would play important roles as they are the ones in charge and would have a say in whether Bella can truly join them or not. Also, the Cullens might still be part of the story, especially Edward, as his relationship with Bella could be a factor in her decision to join the Volturi.
One possible plot could be that Edward is wrongly accused and is in jail. His friends outside start an investigation to prove his innocence. They might face many obstacles like uncooperative witnesses or a corrupt system.
In this fanfiction, Daisy might have some initial struggles to fit in with the Avengers. She could be from a different background or have a different approach to fighting. But as time goes on, she starts to bond with the team members, like sharing combat strategies with Black Widow or having a friendly rivalry with Thor in terms of strength. And she eventually becomes an integral part of the team.