There might be a fanfiction where Bella initially resists the imprint. She's used to her own life and the idea of being imprinted on by Sam might be overwhelming. But as the story progresses, she starts to understand the depth of the connection and how it could bring new meaning and protection to her life. The story could explore her internal struggle and the changes in their relationship over time.
Another theme is the reaction of the pack. In a lot of these fanfictions, the pack has to adjust to Sam being imprinted on Bella, which can cause some conflict and interesting dynamics within the group. It's not always easy for them to accept this new situation.
The main characters are clearly Jacob, Sam, and Bella. Jacob is a werewolf who has imprinted on Bella. He is often portrayed as passionate and protective. Sam is also a werewolf and his imprinting on Bella creates a lot of the story's conflict. Bella, of course, is the human at the center of this supernatural love triangle. She is known for her strong will and her connection to the vampire world as well, which adds more complexity to the story.
There are numerous Bella Sam imprint fanfictions out there. A great one is 'The New Path' which shows how their relationship evolves over time. It starts with the confusion of the imprint and then progresses into a deep, loving connection. Some fanfictions focus on the reactions of the pack to Sam's imprint on Bella, like 'Pack Reactions to Sam and Bella' which adds an interesting layer to the story.
One fanfiction shows Bella being in danger from a powerful vampire. Sam risks his life to save her. Their imprint makes him even more determined. In the end, after the danger is over, they decide to leave the town for a while to explore the world together. They find a peaceful place to settle down and are very happy, with their relationship growing stronger every day because of the imprint.
One possible plot could be the complex love triangle that forms. Jacob and Sam both having imprinted on Bella would lead to intense jealousy and rivalry between them. They might constantly compete for Bella's attention, while Bella is caught in the middle, trying to figure out her own feelings for both of them.
You can start by looking on fanfiction.net. It has a large collection of Twilight - related fanfictions, including those about Bella and Sam's imprint. Another great place is Archive of Our Own (AO3). It's known for its wide variety of fan - created content and has a good selection of these types of stories as well.
There's also 'Sam and Bella: The Imprint Connection'. In this fanfiction, it delves deep into the concept of imprinting and how it affects not just Sam and Bella, but also those around them. It has some great character development and a really engaging plot.
There's a fanfiction called 'Twilight's New Bonds' that deals with Paul and Sam imprinting on Bella. It dives deep into the emotional turmoil that Bella experiences when faced with this unique situation. It also explores how the pack dynamics change as a result.
You can try Archive of Our Own (AO3). It has a vast collection of fanfictions, and there are likely to be several stories about Paul and Sam imprinting on Bella there.