Well, one possibility could be that Naruto, with his ninja skills and strong sense of justice, joins Slade for a common goal like fighting a greater evil that neither could face alone. Maybe they team up to take on a powerful, shadowy organization that threatens both their worlds.
Maybe a new character created specifically for this fanfic. A powerful sorcerer who wants to use Naruto's chakra and Slade's combat expertise for his own evil purposes. He could be manipulating events from the shadows, pitting Naruto and Slade against each other at first until they realize they are being played.
In a fanfic where Naruto joins Madara, it could start with Madara convincing Naruto that his way of achieving peace is more efficient. Madara might show Naruto the dark underbelly of the ninja world that has been hidden from him. Naruto, being the naive but kind - hearted person he is, could be swayed into thinking that Madara's extreme methods are necessary for a long - lasting peace. But of course, this would lead to a lot of internal conflict within Naruto as he goes against his friends and the village he loves.
If Naruto joined Sound in a fanfic, it would completely change the Naruto universe. His relationships would be flipped. Instead of being with Konoha friends like Sasuke and Sakura, he'd be among Sound ninjas. His training might take a different turn too, perhaps learning more brutal and underhanded techniques. This could also lead to a different set of battles and power dynamics in the story.
One possibility is that Naruto could bring a new sense of unity to Mist Village. His never - give - up attitude and ability to make friends might inspire the shinobi there. He could also learn unique Mist Village jutsu and combine them with his own skills, creating new and powerful fighting styles.
A plot twist could be that Slade has an ulterior motive for training Naruto. Maybe he plans to use Naruto as a weapon against Konoha in the future. He might be secretly feeding information about the village's defenses to an enemy while training Naruto. So, when Naruto discovers this, he has to find a way to stop Slade and also deal with the fact that he has been unknowingly part of a scheme against his own home.
He could meet Konan. Since Konan is an important figure in Amegakure, Naruto might have some interesting interactions with her. They could exchange ideas about peace and the future of the ninja world.
Naruto's friends might be initially suspicious of the new skills and attitude he gets from Slade's training. For example, Sasuke could see Naruto's new combat style as too ruthless and this could create tension between them. Sakura might worry that Naruto is getting too influenced by a dangerous figure. However, if Naruto can show that he's still the same person at heart, they could gradually accept his new abilities.
Well, one possible plot could be that Naruto, disillusioned with the Hidden Leaf Village after some major betrayal. He might start to see the Akatsuki's goals in a different light. For example, if the village wrongly accuses him of a crime he didn't commit, like they did with Sasuke in some ways. He could then be approached by an Akatsuki member who offers him a place in the group where he feels he can be understood. And Naruto, in his search for a new purpose and a place to belong, decides to join.
In this fanfic, Naruto might face tougher and more secretive missions. He could be trained in new and deadly ninja techniques specific to ANBU. Also, his relationships with other characters might change. For example, he might become more distant from his old friends as ANBU work often requires secrecy.