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 theme is friendship. Despite their different backgrounds and past enmity, they form a strong bond. This bond is usually tested through various trials and tribulations in the story. It shows that even the most unlikely people can become friends.
One common theme is the exploration of a different kind of relationship dynamic. Since Sasuke is female in this fanfic concept, it can lead to a more nuanced exploration of emotional bonds. For example, it might focus on how their friendship evolves into something deeper in a different way compared to the original series. Another theme could be the struggle with identity. Naruto might have to come to terms with his feelings for a female Sasuke, which could be a big shift from his usual relationship with the male Sasuke in the canon. Also, the fanfic could explore how the avatar - Naruto in this case - uses his powers in relation to this new relationship, perhaps having to protect a more vulnerable - in some ways - female Sasuke.
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 exploration of different cultures within the two series is also a theme. Naruto has its ninja culture with clans and jutsus, while D Gray - Man has the religious - inspired elements of the Black Order and the concept of the Innocence. Fanfics might show how the characters from one culture react to the other, and how they can learn from each other's values and ways of life.
In these fanfics, a key theme is definitely the power of relationships. Since the bond is 'thicker than blood', it shows how strong connections can be formed even across time and different circumstances. Also, the theme of self - discovery is often present. The time - traveling character discovers new aspects of themselves as they interact with the Naruto characters and face the challenges of the past or future. Additionally, the theme of sacrifice can be explored, as the character may have to sacrifice something from their original time or self to protect those new, deep relationships.
One possible theme could be the clash of different power systems. Naruto has his chakra - based powers and Hela has her Asgardian might. Their interactions in a fanfiction might explore how these powers interact. However, since this is a rather unique crossover, it's hard to say exactly what the main themes would be without actually reading a lot of such fanfics.
One common theme is redemption. Nagato has done some cruel things, and in the fanfic, Naruto could be the catalyst for his redemption.
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.
One common theme is redemption. Since Nagato has a complex and often dark past, many fanfictions focus on how Naruto can help female Nagato find redemption. Another theme is the power of friendship or love. The idea that Naruto's positive attitude can influence female Nagato and change her for the better is quite popular. For example, their relationship might start rocky but gradually turn into something beautiful.
One main theme is identity. Harry has to re - evaluate who he is when he discovers he's Voldemort's heir. Another theme is power. Since Voldemort was a very powerful wizard, there's often exploration of whether Harry will inherit some of that power and how he'll use it. And of course, there's the theme of acceptance or rejection by the wizarding community.