Well, it could develop in many ways. Maybe at first Aro is a bit shocked and doesn't know how to handle having a daughter. But as the story progresses, he might start to show a more protective side towards Bella. He could use his power and influence to keep her safe from the dangers in the vampire world.
Bella's character might become more confident. Knowing she has a powerful brother like Aro could give her a sense of security. She may also become more assertive in vampire society.
One possible plotline could be the discovery of their relation and how it shakes up the vampire world. For example, Aro might be more protective of Bella than he is of other vampires. Another could be Bella having to navigate the Volturi politics because of her newfound family tie.
One common theme is identity. Since Bella is Aro's daughter, she often has to figure out who she really is in relation to her father and the vampire world. For example, in many stories, she has to decide whether to embrace her father's ways or carve out her own path.
One possible scenario in such a fanfiction could be that Jasper has to protect Bella in a more paternal way. This could lead to some heart - warming moments where he teaches her about their vampire world, or how to control any emerging vampiric instincts. Also, it would change the love triangle dynamic that exists in the original story. Edward might have to deal with Bella in a different way, not just as a love interest but as someone who is like a sister to one of his family members.
One idea could be that this relationship creates a huge power dynamic shift in the Volturi world. Since Bella is Aro's daughter, she might have unique powers or a special status that Caius is attracted to. It could also lead to a lot of internal conflict within the Volturi, as some may see her as an outsider despite her relation to Aro. And her relationship with Caius might be a way for her to gain more influence and change the Volturi's ways from within.
There's a possibility that she inherits a modified form of Aro's power. For example, instead of just reading minds, she can sense strong emotions through a person's thoughts. This would be a unique power that combines the aspects of Aro's mind - reading and her own empathetic nature. It could also help her in dangerous situations, like sensing when someone has malicious intent towards her.
In this scenario, Bella's life would be full of political intrigue. She'd be caught between her father Aro's expectations and her relationship with Caius. Her relationship with Caius might not be a smooth one at first. They might have to overcome their differences, like Caius' traditional views on vampires and Bella's more modern or human - influenced ideas. But as they grow closer, they could start to change each other's perspectives.
In the long run, this new relationship could lead to new alliances or conflicts. Maybe other vampires would try to use Bella's connection to Jasper for their own gain. Or perhaps Bella and Jasper would form a strong bond that would help them face any threats to the family together. It all depends on how the author wants to develop the story.
One popular 'bella daughter of aro fanfiction' might be 'Bella's New Beginning'. In it, Bella as Aro's daughter discovers her unique powers and has to navigate the complex vampire world. It has interesting character developments and a great plot twist.