Zabuza could be portrayed as more of a mentor figure. Instead of just being a ruthless assassin, he could be shown guiding Naruto in some aspects of combat or strategy. Maybe he survived his encounter with Kakashi and had a change of heart, and now he imparts his knowledge to Naruto who is now a sensei himself.
One idea could be that Naruto, as a sensei, takes on a student who has a similar past to Zabuza. He uses his knowledge of Zabuza's story to teach the student about redemption. For example, Naruto could tell the student how Zabuza was once a feared assassin but had a side that was capable of love and loyalty, as seen with Haku.
Zabuza could be quite cold to Naruto at the beginning. He's not exactly the warm - and - fuzzy type. But when Naruto shows his skills and tells his story of being banished unjustly, Zabuza might empathize on some level. He might not show it openly, but he could start to protect Naruto in his own way, perhaps because he sees a bit of his younger self in Naruto who was also wronged by the ninja system.
He could learn Zabuza's signature water - style jutsu, like the Hidden Mist Technique. This would give Naruto an advantage in terms of creating diversions and hiding his movements during battles.
On a more practical level, Naruto's skills might be misused. Instead of using his power to protect Konoha and the people he cares about, he's using it for Zabuza's self - centered motives. This could also make him a target for other ninja who oppose Zabuza. So not only is he in danger from the people he used to call friends, but also from new enemies. And if he ever tries to break free from Zabuza, he might face severe retaliation from Zabuza himself, which could be life - threatening.
In the fanfiction, Naruto's new sensei could be a mysterious figure who has ties to the Sage of Six Paths. This person might have been waiting for the right time to appear and train Naruto. They could possess knowledge about the origin of chakra and how to fully unlock Naruto's power. It could also be someone who was once an enemy but has now changed their ways and wants to use their skills to train Naruto for the greater good of the ninja world.
There's a chance that Naruto's new sensei could be a self - taught ninja who has developed their own unorthodox style. This person sees Naruto's ability to think outside the box and wants to refine that in him. They could introduce Naruto to a new way of looking at chakra control and combat strategies that are completely different from what he has been taught so far.
There might be. Fanfiction is full of creative and sometimes unexpected ideas. This concept could bring a whole new dynamic to the Naruto story. It could potentially rewrite parts of Naruto's past, like if Zabuza was involved in his early life in some way. Or perhaps it could create a different kind of bond between Naruto and the Hidden Mist Village, since Zabuza was from there.
In most traditional 'Naruto' lore, Naruto has no relation to Zabuza. However, in fanfiction, the author can create any alternate reality they like. So, it's possible for Naruto to be Zabuza's son in some fan - made stories. But this goes against the original story's character backgrounds and relationships.
I think Orochimaru would be the most unexpected sensei. Usually, he's seen as a villain, but in a fanfiction, if he were to train Naruto, it would be extremely unexpected. He has a vast knowledge of jutsu, especially forbidden ones. He could teach Naruto some very powerful and unique abilities, but at the same time, Naruto would have to deal with Orochimaru's morally ambiguous nature.