One key element is the unique relationship dynamics. Bella's relationships with Marcus and Alistair are different from the normal vampire - human relationships. It's often about exploring new kinds of love and loyalty.
One popular 'Bella Swan Marcus and Alistair mates fanfiction' is 'The Unlikely Bond'. It explores the unique relationships that form between them in an interesting way.
One common theme is the struggle to adapt to their new relationship. Since Bella was initially involved with other characters in the Twilight series, her being mates with Alistair can bring about a lot of internal conflict.
Yes, there are quite a few. You can start by looking on popular fanfiction websites like Fanfiction.net or Archive of Our Own. Just search for 'bella swan and alistair mates' and you'll likely find some interesting stories.
One key element is often the exploration of a new relationship dynamic. Since they are not a canon pairing, it's interesting to see how they interact. Another element can be the alteration of the existing story's setting to fit their relationship.
Love is a major theme. Their bond as mates is a form of deep, fated love. Another theme is discovery. Bella and Alistair often discover new things about themselves and their powers through their relationship.
One great 'Bella and Alistair are mates' fanfiction is 'Destined Bond'. In it, Bella discovers her connection with Alistair in a very unexpected way. They meet during a magical storm and from that moment, their lives are intertwined. The story beautifully depicts their journey as they learn about each other's powers and pasts.
The theme of sacrifice is also quite prevalent. For example, they might sacrifice their own desires or opportunities for the sake of their relationship. Also, the theme of family acceptance. Sometimes their relationship is not initially accepted by their families, and they have to work through that.
Another plot could be that they are on opposite sides of a conflict initially. But as they realize they are mates, they have to find a way to reconcile their differences and work together. This could involve a lot of internal struggle for both of them as they deal with loyalty to their respective sides and their new - found bond.
One key element is the deep emotional connection. Since they are mates, there's this intense bond that is often explored. Another is the struggle against the norms of the vampire - human relationship in the 'Twilight' world.
One key element is the transformation of their relationship. In the original story, their relationship is complex, and in fanfiction, it often evolves in different directions. Another is the werewolf lore. Writers often expand on the werewolf aspects related to Jacob, which affects his relationship with Bella.