One common theme is the combination of different elemental powers. Since Naruto has his own set of abilities related to chakra and Korra is an Avatar with control over four elements, fanfics often explore how these powers can work together or create new forms of combat.
The theme of friendship and mentorship also pops up a lot. Given their different levels of experience (Naruto being very experienced by the end of his series and Korra being younger and still learning), fanfics may explore how Naruto can be a mentor to Korra, or how they can form a strong friendship based on mutual respect and learning from each other's strengths and weaknesses.
Another theme is the cultural exchange. Naruto comes from a ninja - based culture, while Korra is from a world with a more Asian - inspired Avatar - centric culture. Fanfics might show how they introduce their respective cultures to each other and how their friends and allies react to it. For example, Naruto might introduce his friends to the concept of the Avatar and Korra could show Naruto's gang some unique traditions from her world.
Another theme is the origin of ninja techniques. Fanfics might focus on how the First Hokage developed his signature jutsu, like his powerful wood - style techniques. They might also explore how he passed on his knowledge or if there were any secrets behind his abilities. This can add a lot of depth to the story as it ties in with the overall Naruto universe's focus on jutsu development.
Power and its limits. When Naruto characters enter the Fate universe or vice versa, they have to figure out how their powers stack up. For instance, Naruto's huge chakra reserves compared to the magic in Fate Stay Night.
Another theme is teamwork across universes. Characters from RWBY and Genlock have to come together, and this brings up issues of trust, communication, and understanding. They have different backgrounds, goals, and ways of doing things. In some fanfics, they initially struggle to work together but gradually learn to appreciate each other's strengths. This theme is important as it shows how different individuals can overcome their differences for a common good.
One main theme is power. Since both Naruto and Highschool DxD have characters with different levels of power, in the fanfic, it's often about how Naruto's power compares and combines with the powers in the DxD world. Another theme is friendship. Naruto is all about friendship, and in the DxD world, there are also relationships to be formed and maintained.
Identity is also a big theme. Since the fox transformation is such a big part of Naruto, fanfics will look at how this transformation affects who he is, whether he's seen as more of a monster or a hero because of it. For example, in some fanfics, his friends have to come to terms with this new, more powerful and somewhat wild - looking Naruto. And it really makes for an interesting exploration of relationships as well.
One common theme is the idea of opposites attract. John and Karkat have very different personalities, and fanfics often play on how these differences can actually bring them together in a unique way.
Power and self - discovery are also frequently explored. Shihoin may start out with certain abilities but then uncovers new powers or aspects of themselves as the story progresses. For example, in some fanfictions, Shihoin has to learn to control a new and powerful jutsu. This theme ties in with the overall theme of growth that is prevalent in the Naruto series.
One common theme is the clash of cultures. Since Naruto's world has its own set of values, ninja clans, and a unique power system, and Highlander has its own lore about immortals and their rules. When combined, it often leads to exploring how these different cultures interact and adapt to each other.
One main theme is redemption. Nagato has done a lot of bad things in the Naruto series, and in fanfics, often Naruto is the catalyst for his redemption. For example, Naruto's talk - no - jutsu can make Nagato see the error of his ways.
Another common theme is self - discovery. They might each go through a journey of finding out more about themselves while also being there for their friend. For example, Maxxie might be exploring his identity in the world of fashion and dance, and Anwar could be on a path of finding his own voice in different areas like music or academics, all while relying on their friendship as a support system.