A common theme is the clash of two different worlds. Elsa comes from a world of magic and royalty, while Naruto is from a world of ninjas and shinobi clans. So, the fanfictions often explore how these two very different cultures interact.
Many 'Elsa and Naruto' fanfictions also deal with the idea of isolation. Elsa has her own isolation in her story due to her powers, and Naruto was also somewhat isolated as a child. Fanfictions might explore how they can understand each other's feelings of loneliness and help each other overcome it.
One possible plot could be that Naruto, being Elsa's son, discovers his ice powers at a young age in the Hidden Leaf Village. He might struggle to control them at first, just like Elsa did. His friends in the village could be both curious and a bit scared of his powers. Naruto would then have to learn to balance his ninja training with understanding and mastering his ice abilities, all while trying to keep his identity as Elsa's son a secret from potential enemies who might want to use his unique powers for their own gain.
A really cool fanfiction idea could be that Naruto and Elsa are both summoned by a powerful sorcerer in a different dimension. They have to work together to find a way back home. Along the way, they discover that their powers are connected in some way, like Naruto's chakra can enhance Elsa's ice powers and Elsa's ice can be used to create new jutsu for Naruto.
I'm not really into that kind of crossover lemon fanfiction, but you can try searching on some fanfiction websites like Archive of Our Own. Just be aware that not all such content may be appropriate or well - written.
One possible plot could be that Naruto somehow ends up in Elsa's world and they initially have a misunderstanding but then gradually develop an attraction. And then, in a rather inappropriate way for non - lemon versions, there could be some romantic and more adult - themed interactions.
One possible plot could be that Naruto, while on a strange mission, gets transported to Elsa's world. Naruto, being his adventurous self, tries to understand Elsa's powers and her fear of them. He might encourage her to face her fears in a more direct way, like he does with his own challenges in the ninja world. And they could team up to protect Elsa's kingdom from some unknown threat.
In the long run, Elsa's powers could inspire new Ninja techniques. Ninja are always looking for ways to improve their abilities, and seeing Elsa's ice powers might give them ideas for new ways to manipulate chakra to create similar effects. This could lead to a whole new branch of Ninja techniques. And as she becomes more involved in the Naruto plot, her powers could be the key to defeating a major villain that the regular Ninja techniques are not enough to handle. For example, if there was a villain who was immune to normal attacks but vulnerable to extreme cold, Elsa's ice powers would be crucial in the final battle.
One popular Elsa Naruto fanfiction is 'Frozen in the Ninja World'. It combines the magic of Elsa from 'Frozen' with the ninja world of Naruto in an interesting way. The story often has Elsa trying to adapt to the new and strange ninja environment while also using her ice powers to help or sometimes cause trouble in the Hidden Leaf Village.
Naruto's Rasengan could be encased in Elsa's ice to create a more powerful and destructive attack. The ice would make the Rasengan even more solid and increase its impact.