Common themes include identity. The Rez Girl might be trying to find her place within her own culture and in the outside world, and Jacob could play a role in that. Also, family is often a theme. The Rez Girl's family and their traditions could impact her relationship with Jacob. It could be that her family has certain expectations that she has to balance with her feelings for Jacob.
One common theme is cultural exchange. Jacob gets to learn about the Rez Girl's culture and she might learn about his. Another theme could be love against odds, as they may face difficulties due to their different backgrounds.
Fanfiction about Jacob and a Rez Girl can be quite diverse. Some stories might be more focused on adventure, with the two of them going on quests around the reservation area. Others could be centered on their emotional connection. For example, they might start off as strangers but gradually develop a deep bond as they share their stories and dreams. The Rez Girl's connection to her native culture can also be a major part of the story, like she might teach Jacob about her tribe's ancient stories or spiritual beliefs.
One common theme is the struggle between their different natures. Jacob is a werewolf and Nessie is part - vampire, so there can be a lot of tension regarding their instincts. Another theme is loyalty, as they are both loyal to their families and groups.
One common theme is the love triangle between Jacob, Bella, and Edward. Many fanfictions explore how Jacob's feelings for Bella develop and how she navigates her relationships with both of them.
A major theme is loyalty. Jacob is extremely loyal to Nessie, and this is shown in many fanfictions. They also often explore the theme of family. Jacob becomes like family to Nessie, and how that dynamic affects their relationship is a big part of these stories. Additionally, the theme of power is there as Nessie has unique powers that she has to learn to control, with Jacob sometimes being involved in that process.
Another theme is growth. As they are both young in the story, fanfictions often show how they grow both individually and as a couple. For example, they might learn how to deal with their unique powers and how that affects their relationship.
One common theme is friendship. Their bond is often explored, like how they rely on each other in difficult times.
A theme that is not so obvious but still present is the idea of belonging. The OC, being an original creation, often has to find their place in the world where Jacob already has his own role. This exploration of where they fit in relation to each other and the world around them is quite common in these fanfictions.
One common theme is unrequited love. In many fanfictions, Jacob's love for Bella is often not fully reciprocated in the way he hopes, leading to a lot of angst. For example, in some stories, Bella is still torn between Jacob and Edward, which creates a lot of emotional turmoil for Jacob.
One common theme is Jacob's struggle with his identity. As a werewolf in the Twilight series, he has to deal with his dual nature, and many fanfictions expand on this internal conflict. Another theme is his relationships, especially his complex relationship with Bella. Fanfictions often explore the unrequited love or the deep friendship between them.
One common theme is the exploration of their different natures. Jacob being a werewolf and Carlisle being a vampire. Writers often play with how they overcome their natural enmity and form a relationship.