Well, a plot could revolve around Carlisle and Bella having to work together on a school project at Forks High School. During this time, they start to understand each other on a deeper level. Maybe Bella discovers some long - lost medical knowledge that Carlisle had forgotten from his past, and this helps him in his work at the hospital. It could also be a story where Bella has a premonition about Carlisle getting into trouble and she has to convince him to believe her.
One idea could be exploring how they handle the reactions of the Cullen family. Some might be happy for them, while others could be a bit skeptical at first. Another plot could involve Bella learning more about Carlisle's long past and how it shapes their relationship. They could also face challenges from the vampire world due to their unique union.
One idea could be Carlisle having to protect Bella from a new vampire threat that is specifically targeting her for her unique connection to the Cullens. Maybe a group of nomadic vampires who are jealous of the Cullens' lifestyle.
Alice would be a great character to include. Since she can see the future, she could add an element of mystery and foreshadowing to the side story. For example, she could give hints about the relationship between Carlisle and Bella that they themselves haven't realized yet. Jacob could also be included. His werewolf nature could contrast with Carlisle's vampire nature, creating some interesting interactions especially if they both have an interest in Bella's well - being.
In this type of fanfiction, a great plot could be that Carlisle and Esme discover Bella has a prophetic dream ability. This ability makes her very valuable in the vampire world as she can foresee potential threats. However, it also makes her a target. Carlisle and Esme must then train Bella to control her power while also keeping her safe. Additionally, the family dynamics could change as Bella becomes closer to them. She might start to change some of their long - held beliefs about humans and vampires, and this could lead to internal family discussions and growth.
A plot could revolve around Carlisle and Bella going on a secret mission together. Maybe they have to find a lost ancient vampire artifact that could change the future of the vampire world. Along the way, they develop a deep bond and respect for each other.
A possible plot could be that there is a threat to the vampire community that only Bella and Carlisle, with their combined skills and knowledge, can solve. As they work together, they start to see each other in a different light. Carlisle might see Bella not just as a young vampire but as a strong and intelligent equal, and Bella could gain a deeper respect for Carlisle's wisdom and experience. During this time, their relationship could evolve in unexpected ways, like a deeper friendship that is on the verge of something more, but they are hesitant due to the age gap and their different roles in the vampire family.
One plot idea could be the internal struggle they face within the vampire community. Since vampires usually have a monogamous mate concept, the three of them being mates would be a huge deviation. They might have to deal with the judgment and envy of other vampires. Another idea is exploring how they protect each other from outside threats. For example, a new vampire coven that doesn't accept their unusual relationship might try to harm them. And also, their daily life together could be full of interesting moments like sharing their different experiences from their long vampire lives.
One interesting plot twist could be that Bella discovers she has a hidden power that not even Carlisle expected. This power might change the way she interacts with the vampire world and her role within the Cullen family.
One idea could be Percy getting involved in the vampire - human drama in Forks. Maybe he discovers the secret of the Cullens and tries to find a way to co - exist with them, given his own experiences with different species in his own world.
One idea could be that Bella has a brief encounter with someone before arriving in Forks and discovers she's pregnant. She then has to deal with the shock and the secrecy while also starting a new life in Forks. Maybe she's worried about how the townspeople will react and how it will affect her future relationship with Edward, if she still meets him in this scenario.