I think Naruto, Aang, and Zuko would be great characters to focus on. Naruto and Aang for the reasons mentioned before, but Zuko adds an interesting element. His journey from a villain - like figure to a hero in the Avatar world could contrast with Naruto's own journey of being an outcast turned hero. They could all have great character development as they interact and face challenges together.
In my opinion, Sakura from Naruto and Katara from Avatar: The Last Airbender would be interesting. Both are strong - willed female characters. Sakura's medical ninjutsu could be compared and perhaps combined with Katara's waterbending skills. They could also bond over their experiences of being part of a team and having to prove themselves in a male - dominated world of fighting and power.
Well, a cool plot might involve Naruto being transported to the Avatar world. He gets mistaken for a powerful bender at first. As he tries to figure out how to get back home, he helps the Avatar and his friends in their fight against the Fire Nation. Along the way, Naruto teaches them some of his ninja skills like stealth and quick combat moves, and in return, he learns about the different types of bending. Maybe there could be a big showdown where Naruto's Rasengan combines with Aang's airbending to defeat a huge threat.
Aang is really interesting. He's the Avatar, so he has this huge responsibility on his shoulders at such a young age. He's fun - loving yet has to deal with the serious task of stopping the Fire Nation. Zuko is also fascinating. His internal struggle between his loyalty to his family and what he knows is right makes his character complex.
A 'Dark Naruto Avatar The Last Airbender Fanfic' has the potential to be a thrilling read. Picture Naruto being influenced by the power - hungry villains in the Avatar universe. His transformation into a darker version could bring about a war between the ninja world and the Avatar world. His Rasengan could be combined with some form of bending, creating unique and powerful attacks. The fanfic could also show how the values of the two worlds clash when Naruto goes dark, and how the heroes of both universes have to come together to stop him.
Zuko is extremely popular as well. His complex character arc, from being a villain - like figure to a hero, is very engaging. People love to see his transformation and how he overcomes his inner demons and the expectations of his family and nation.
Sakura from Naruto is often included in these crossovers as well. Her skills as a healer and her growth as a strong female character can add depth to the crossover stories. She could potentially learn new forms of healing from the Avatar world or teach her own medical ninjutsu to Avatar characters.
Aang is often a popular choice. Genderbending him can lead to some really interesting storylines, like how a female Aang would handle being the Avatar in a male - dominated world of bending. Another popular one is Zuko. Changing his gender can add a whole new layer to his character arc, especially his relationship with his father and his journey of self - discovery.
In this kind of crossover, Gaara could be a fascinating character to focus on. His ability to control sand could be used in really creative ways against the zombies, like creating barriers or using sand - based attacks. From 'The Walking Dead', Michonne would be great. Her katana - wielding skills are similar to the ninja sword skills in the Naruto world, and she could learn some new moves from the ninjas. Also, Naruto's teacher Jiraiya. His knowledge of various jutsus and his overall wisdom could be key in coming up with strategies to deal with both the zombies and any new threats that come from the crossover of the two worlds.
Definitely Ben Tennyson himself. He has a whole range of alien forms and abilities, and seeing how he would adapt to the Avatar world would be really cool. For instance, how would he use Four Arms in a fight against earthbenders or how would he use XLR8's speed in a chase through the air temples.
Naruto and Aang would be a great pair. Aang's carefree and spiritual nature could contrast with Naruto's more boisterous and determined personality. They could learn a lot from each other. Naruto could teach Aang about never giving up on your dreams in a more direct and aggressive way, while Aang could show Naruto how to be more in tune with the spiritual side of things.
It's hard to say for sure without reading it, but likely Aang would still be a main character. He might be older and facing new challenges. Katara could also be a main character, perhaps with her waterbending skills being even more refined. Zuko too, as he continues to deal with the Fire Nation's future.