One idea could be that Jack Frost from 'Rise of the Guardians' visits Arendelle during a particularly harsh winter. He meets Elsa and they both discover that they have a unique connection to winter. Maybe Jack can teach Elsa some new tricks about controlling snow and ice, and in return, Elsa shows Jack how she uses her emotions to create beautiful ice sculptures. They could team up to save Arendelle from an even greater threat, like a dark force that wants to plunge the kingdom into eternal winter.
The clash of different power systems. In Naruto, there are chakra - based ninjutsu, while in Rise of the Guardians, there are more magical, elemental powers. When these collide in a crossover, it can create really cool fight scenes. For example, Sasuke's Sharingan against Jack Frost's ice powers.
A common theme in 'rise of the guardians crossover fanfiction' is the clash and then the resolution of different personalities. You have the Guardians, who are all unique in their own ways, and then you bring in characters from other stories with their own distinct personalities. At first, there might be clashes due to differences in beliefs or ways of doing things, but eventually, they work together. This theme of overcoming differences to achieve a common goal is very common in these crossovers.
One popular 'Naruto Rise of the Guardians crossover fanfiction' might be those that focus on Naruto characters gaining the powers of the Guardians. For example, Naruto could get Jack Frost's power over ice and snow, which would completely change the dynamic of his battles in the Naruto world. It could also lead to interesting interactions with his friends and foes as they try to understand this new power.
In a 'naruto rise of the guardians fanfiction', the story could be a crossover where the characters from Naruto and the Guardians meet. Naruto and his comrades may be called upon to help the Guardians in their fight against some dark force. The fanfiction might play with the idea of Naruto's ninja skills and the Guardians' unique powers working together. For instance, Sasuke's Sharingan could be used in combination with the Guardian of Dreams' power to enter and manipulate dreams. It could also show how the values of the Naruto characters, such as friendship and perseverance, are applied in the context of the 'Rise of the Guardians' world.
One challenge is combining the different magic systems. In 'Rise of the Guardians', the magic is more about the Guardians' individual powers and beliefs. In 'Frozen', Elsa's magic is closely tied to her emotions. Writers need to figure out how these two types of magic can interact without seeming too forced. For example, how can Jack Frost's power of cold and snow blend with Elsa's ice - creating powers in a believable way.
Most likely Naruto would be one of the main characters. Since it's a Naruto - based fanfiction, he'd probably be at the center of the story. And maybe some of the Guardians from 'Rise of the Guardians' would also be main characters, like Jack Frost.
A crossover with 'Frozen' might also be cool. Imagine Jack Frost interacting with Elsa. They both have ice - related powers, so it could explore how their powers compare and contrast. There could be a story where they help each other understand and control their abilities better.
One popular crossover is with 'How to Train Your Dragon'. The idea of the Guardians interacting with the Vikings and dragons makes for some really exciting stories. Another is a crossover with 'Frozen'. The contrast between the cold - themed worlds and the different powers of the characters can lead to very interesting plotlines.
You can start by looking on popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions, and you can use the search function to specifically look for 'rise of the guardians crossover' works. Another option could be Fanfiction.net, though the interface and categorization might be a bit different.