The plot could involve Caius hiding his true identity from Bella for a long time. She might grow up thinking she has a normal father, until strange things start to happen. For example, she notices that her father never ages. Then, when she discovers the truth, she has to come to terms with being part vampire herself. Caius would then have to protect her from those who might want to harm her because of her unique heritage.
In such a fanfiction, it could completely change the dynamics of the Twilight universe. Caius, being a powerful and somewhat cruel vampire in the Volturi, as Bella's father would bring a whole new set of storylines. Maybe he would be overly protective in a very different way compared to Charlie. He might use his vampire powers to keep Bella in a sort of 'gilded cage' for her safety, which could lead to a lot of conflict with the Cullens and other characters. It could also explore how Bella's character would develop differently, growing up with a vampire father and the knowledge of the vampire world from a very different perspective.
One possibility could be that their baby has unique powers. Since Bella has her own set of abilities and Caius is from a special vampire lineage, their child might inherit a blend of powers. For example, it could have super strength like vampires but also an enhanced mental connection like Bella's gift. The story could then focus on protecting this child from those who might want to use its powers for their own gain.
Well, it could start with Bella being captured by Caius. As his pet, she is forced to live in his lair. Caius might be possessive of her and not allow her to interact with others. Bella, being a strong - willed character, tries to resist this new role. She could start to learn about Caius' past and weaknesses in order to find a way to break free. There could also be a love - hate relationship developing between them, where Caius starts to have unexpected feelings for Bella as more than just a pet, which further complicates the situation.
She could inherit enhanced strength. Caius is a powerful vampire, and strength is a common trait in vampire bloodlines. So Bella might be able to overpower other vampires or supernatural beings more easily.
In the 'damon is bella's father fanfiction', it could start with Damon having a strange feeling that he has a connection to someone. As he investigates, he finds out about Bella. Their relationship could be filled with misunderstandings at first. For example, Bella might be resentful that he wasn't there for her growing up. But over time, they could learn to understand each other. Damon could introduce Bella to his world, whether it's a world of magic or some other extraordinary place, and they could form a strong bond.
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.
Well, Caius could be very possessive and see Bella's blindness as something that makes her even more his. He would be by her side all the time, guiding her physically when needed. He might also share his vampire senses with her in some way, like describing the world around them in vivid detail so that she can 'see' through his words. And he would definitely be very angry if anyone made fun of or took advantage of her blindness.
One possible plot twist could be that Bella discovers Caius has a hidden agenda all along, and it's not just about their relationship. Maybe he's using their bond to gain power within the vampire world. Another twist might be that Bella has a secret power that is awakened by her connection with Caius, and this power changes the dynamics of their relationship and the entire vampire community.
At first, it might be a bit rocky. Bella, being human and now blind, is in a very vulnerable state. Caius, as a powerful vampire, may come off as intimidating. But as time goes on, they start to develop a deep bond. Caius learns to be more gentle and caring, and Bella starts to trust him more and more.
There could be a story where Caius has a change of heart after meeting Bella. In the Twilight world, Caius is known for his strict and often cruel ways. But when he encounters Bella, he starts to question his own beliefs. Maybe Bella gets lost in the Volturi territory and Caius finds her. Instead of punishing her, he is intrigued by her. This could lead to a story of him trying to understand her human - vampire relationship with Edward from a different perspective. He might even start to envy Edward in a way, which could create a whole new dynamic in the fanfiction.