Love triangles are a big part of these fanfictions. Bella is in a unique position with Carlisle and Caius. There's also the theme of self - discovery. As Bella navigates this new relationship, she discovers new sides of herself. And the theme of family is there too, as Carlisle has his own family and Caius has his own group, and Bella has to find her place within these complex family structures.
One common theme is the struggle against the odds. Since Bella and Caius are from different 'worlds' in a sense, they often have to face opposition from other vampires or even Bella's human friends. Another theme is the discovery of a deep, new connection. It's about how they come to realize their bond as mates.
One popular 'bella is carlisle and caius mate fanfiction' is 'Twilight Reimagined'. It offers a unique take on the relationships, with interesting character developments.
Many of these fanfictions explore the theme of identity. Harry has his own identity as a wizard, and Caius has his as a vampire. When they become mates, they have to reconcile their identities and find a new combined identity. This exploration of identity makes the stories really interesting.
Power dynamics is another theme. Caius has a certain power, and the OC may or may not have their own powers. The fanfictions explore how these power levels interact and how they influence the relationship, whether it's through protection or a power struggle.
One common theme is the struggle between different vampire clans. Since Caius is part of the Volturi and Bella has her own connections, this often creates a backdrop of power struggles and politics in the fanfiction.
Love and devotion are very common themes. These fanfictions often explore how Carlisle and his mate are deeply in love and devoted to each other, through various situations.
One common theme is the forbidden love aspect. Since Carlisle is a much older vampire and Bella is a young human, there's that sense of something not being allowed, which adds a lot of tension to the stories.
A frequent theme is the exploration of Carlisle's self - control. In fanfictions, his struggle to maintain his composure around Bella, especially given her alluring blood, is often highlighted. Also, the theme of Bella's growth and transformation under Carlisle's influence is common. She may become more confident, more in - tune with the vampire world, and this transformation is central to many stories.
Love against all odds is also a big theme. Caius is part of the Volturi, which makes their relationship controversial. But in many fanfictions, their love overcomes these obstacles. They find a way to be together despite the expectations and rules of the vampire society.
One common theme is identity. Bella has to re - define who she is as Caius' sister instead of just being Edward's love interest. Another theme is family loyalty. She has to figure out where her loyalties lie between the Cullens and the Volturi.