One idea could be that the characters from Avatar: Pandora discover a portal to the Naruto universe. They are amazed by the ninja abilities and chakra system. Some Pandora characters might try to learn ninja techniques, while Naruto characters are intrigued by the unique flora and fauna of Pandora.
Perhaps in this fanfiction, a Pandora character gets lost in the Naruto universe. They end up in Konoha village and are initially seen as a strange being. But Naruto, being the kind - hearted person he is, befriends this character. The Pandora character then shares their knowledge of nature and connection with it, which is somewhat similar to how ninjas use chakra. This leads to new training methods being developed in Konoha, and the Pandora character also learns about ninjutsu and how to use it in their own way.
Well, a great plot could involve a common enemy that threatens both Pandora and the Naruto world. The ninjas and the Pandora natives have to team up. For example, an evil force is draining chakra and the energy of Pandora's nature simultaneously. Naruto and his friends, along with Pandora's strongest warriors, must combine their skills to defeat this foe. They learn from each other's cultures and fighting styles in the process.
Maybe the Avatar, in his journey to master all the elements, travels to the Naruto world. He could learn some ninja techniques and incorporate them into his fighting style. The Avatar could also teach the ninja about the power of bending, which could lead to some really unique team - up strategies among the characters.
Perhaps the nine - tailed fox in Naruto and the Avatar state could have some sort of connection. In the fanfiction, the two powers could interact in unexpected ways. For example, when Naruto enters his nine - tailed fox mode, Aang's Avatar state could be affected, or vice versa. They might have to learn to control these interactions to save both their worlds from a dark force that wants to use this power connection for evil.
In a naruto x avatar fanfiction, there could be a scenario where the Akatsuki from Naruto's world teams up with some of the villains from the Avatar world. This would force Naruto and the Avatar (whichever one it may be) to put aside their differences and form an alliance with other characters from both worlds to stop this powerful and evil coalition.
Perhaps the Akatsuki from Naruto somehow get involved in the Avatar world's politics. Their goals of collecting tailed beasts could be translated into a search for some powerful Avatar - related artifacts. This would stir up a lot of chaos in the Avatar world and force the Avatar and his friends to team up with some Naruto characters to stop them.
A plot could be centered around Zuko from Avatar joining the Straw Hats for a while. He could teach Sanji some fire - bending inspired cooking techniques. Meanwhile, Nami might use her knowledge of weather to help the Avatar characters understand their own natural elements better. And Usopp could create some cool gadgets inspired by the technology and bending in the Avatar world.
Another plot could be that Naruto is mistaken for an Avatar in the Avatar world. As he tries to clear up the misunderstanding, he gets involved in local politics and relationships. The female characters see his honesty and kindness, and gradually, a harem - like situation develops around him.
One idea could be that Naruto somehow gets transported to the Avatar world and his unique ninja skills draw the attention of multiple female characters. They might be intrigued by his determination and power, leading to a harem - like situation where they all vie for his attention.
One idea could be a Spartan from Halo ending up on Pandora. Maybe they team up with the Na'vi to fight off a common enemy, like a new type of alien that's more powerful and dangerous than the Covenant or the RDA. The Spartan could introduce advanced human technology to the Na'vi, which would change their way of life in some aspects. For example, they could use some of the shielding technology to protect their homes. Another plot could involve the transfer of consciousness, like in Avatar, but with a Halo - related twist. Perhaps a character's mind is transferred into an enhanced alien body, similar to the Elites in Halo.
One idea could be a crossover between Avatar: The Last Airbender and Harry Potter. Imagine Aang and his friends attending Hogwarts and learning magic alongside wizardry students. They could use their bending skills in magical duels.
One interesting storyline could be about a human who is stranded on Pandora and has to learn the ways of the Na'vi to survive. They form a bond with a particular Pandora creature that helps them in their journey.