One common theme could be power dynamics. Naruto has his own set of powers, and Jasper and Alice have their unique vampire abilities. So, how these powers interact and who is more powerful in different situations can be a theme. Another might be friendship. Naruto is all about friendship, and seeing how he would form friendships with Jasper and Alice is likely to be explored in such fanfics.
Love and commitment are very common themes. Since it's about their wedding, the focus is often on their deep love for each other and their commitment to a future together.
One common theme is family. It shows how they form a new family unit with the baby. Another is protection. Since they are vampires, protecting the baby from various threats is often a big part of the stories.
One common theme is love at first sight. Since they are meant to be mates in the Twilight universe, many fanfictions play on that instant connection when they meet.
One common theme is the exploration of their relationship in different scenarios. It could be in a more romantic or intense setting. Another theme might be their supernatural abilities and how those play into their interactions, as they are often part of a supernatural world in the original context. Also, themes of loyalty and protection between them are quite prevalent.
Love is a very common theme. Their relationship as humans is often explored in a romantic way.
A lot of these fanfictions might explore the theme of self - discovery within their relationship. As they love each other, they also learn more about themselves. For instance, Alice might discover new aspects of her powers or Jasper might come to terms with his past through his love for Alice. And there could also be themes of family and friendship in relation to their love story, as their friends and family might play important roles in their relationship.
One common theme could be the anticipation and excitement of new life. Since Alice and Jasper are characters, their reactions to the pregnancy would be explored, like Jasper's protectiveness perhaps.
Another theme is the struggle with their vampire nature. They are vampires in the Twilight world, and fanfictions sometimes explore how they deal with things like bloodlust and fitting into the vampire society while maintaining their relationship. It's interesting to see how different authors handle this aspect.
Love and loyalty are common themes. Their relationship is often explored in depth, showing how their love for each other endures through different challenges. For example, in many fanfictions, they face threats from other vampires or difficult situations within the Cullen family, but their loyalty to each other never wavers.
One common theme is friendship. Since Bella becomes part of the Cullen family, fanfics often explore the friendship between her, Jasper and Alice. For example, how they support each other through tough times.