In fanfiction, you can also combine their storylines. Say, the plot of 'The Lion King' could be merged with Naruto's journey to become Hokage. Simba's struggle to take his rightful place as king can be paralleled with Naruto's efforts to gain the respect of the Hidden Leaf Village and become its leader. There could be a common enemy that both Naruto and Simba have to face together, something that threatens both the pride lands and the ninja village.
The settings can be combined too. You could create a new world where the Naruto universe and the remnants of Krypton co - exist. Maybe there's a city in this new world where ninjas and Kryptonians live side by side. Naruto could then explore this new place, learn about Kryptonian technology, and use it to enhance his own ninja tools or techniques.
One way is to have the characters from Naruto join a peerage structure similar to that in Bleach. For example, the Hokage could be like the king of the peerage. Then, the jutsu of Naruto characters can be compared or integrated with the powers in Bleach. So, a Rasengan could be equivalent to a certain level of reiatsu - based attack.
A simple way is to make Naruto encounter an orange - themed Pokemon event. For example, a festival in the Pokemon world that features orange - colored Pokemon like Flareon. Naruto gets involved in the festivities and through that, he meets new friends and gets into some light - hearted adventures.
One way to combine them creatively is to have a Disney princess end up in the Star Wars universe. For example, Belle could be a diplomat on a planet in the Star Wars galaxy, using her intelligence to negotiate treaties. Another idea is to give a Star Wars character the traits of a Disney princess. Maybe Rey could be seen as a kind of 'princess' figure, with her own 'castle' (the Millennium Falcon) and her loyal 'subjects' (her friends).
Another way is to have Naruto fuse his chakra with someone who has the ability to use Susanoo, like Sasuke. They could create a combined form that has the best of both their powers. The story could detail their journey of learning to work together and master this new form.
First, consider the setting. A Naruto - style world could be merged with the pirate - filled seas. The assassin part comes in with the character's motives. He could be an outcast ninja from Naruto's world who finds a new life among pirates but still uses his ninja assassination skills. He might have to fight against other pirate crews or even sea monsters using his Naruto - inspired jutsu and assassin techniques. This combination would create a really unique and exciting fanfiction.
Well, the bright and colorful style of My Little Pony can be blended with the more detailed and sometimes more realistic art of Disney. For example, the soft, rounded shapes of the ponies could be placed in a Disney - like landscape. The big eyes of the ponies could be adjusted a bit to fit the overall look when combined with Disney characters.
In a Naruto EMS Rinnegan One Piece fanfiction, perhaps there is a mysterious island in the One Piece world that is actually a portal to the Naruto world. A One Piece character stumbles upon it and gains the powers of the EMS and Rinnegan. This character then has to learn how to control these new powers while still maintaining their own identity from the One Piece world. They could use the EMS to enhance their observation skills, like a more advanced form of Kenbunshoku Haki, and the Rinnegan to perform powerful jutsu-like attacks that are completely new to the One Piece universe.
Naruto's chakra could interact with the magic in Salem's world in unique ways. For example, his Rasengan might be enhanced by the dark magic there, or his shadow clone jutsu could be used to infiltrate Salem's strongholds in a different way than normal magic would allow.
They can be combined through a portal concept. A portal opens between the Naruto universe and the Transformers universe, bringing Naruto and Arcee together. Then they can work towards a common goal like saving both universes from a threat that spans across dimensions.