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.
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.
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.
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.
It might not be one of the most mainstream ones. There are so many different types of fanfiction, and while some relationships like this can be explored, it may not have as wide an appeal as more common pairings. However, in certain niche groups within the fanfiction world that are focused on specific characters like Bella and Caius, it could be quite popular.
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.
One idea could be that Bella's cousin comes to Forks for a visit. Caius, while on some Volturi business in the area, catches sight of her. He's intrigued by her different scent compared to the other humans in town. Their relationship could start with some tense encounters as Caius tries to figure out why she's so interesting to him.
One plot idea could be that Bella's sister discovers Caius's true nature as a vampire but instead of being afraid, she is intrigued. She starts to secretly study vampires and their lore, and in the process, catches Caius's attention. He then decides to keep an eye on her, leading to a series of tense yet fascinating encounters.
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.
One plot idea could be Bella dealing with a difficult case of a terminally ill child. She could struggle to find a treatment while also providing emotional support to the family.
Well, in some of these fanfics, a common plot point is Caius introducing Bella to the vampire world's unique honeymoon traditions. For example, they might have a special vampire - themed celebration in a secret location. Another plot point could be Bella's struggle to adapt to Caius's more extravagant lifestyle during the honeymoon. She might be used to a simple life, but Caius is used to luxury.