Indeed, Koro Sensei passes away in the manga. This event is both emotional and crucial to the story's conclusion, leaving a lasting impression on readers.
Well, Koro Sensei used to be a human being who worked as an assassin. However, some top - secret experiments were carried out on him by the government. These experiments led to his transformation into a strange octopus - like form. His back story also includes the fact that he has a limited time to live because of the after - effects of those experiments, which is why he becomes a teacher to try and leave a positive mark on his students' lives before his end.
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.
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.
In this fanfiction concept, it could lead to a really interesting dynamic. Jiraiya is a powerful and eccentric ninja. He could teach Naruto some really unique jutsu, like more advanced forms of Rasengan. And their relationship would be filled with Jiraiya's boisterous personality clashing and also complementing Naruto's determination.
In fanfiction, Naruto as a sensei often has a very unique dynamic with his genin team. He might teach them his own unorthodox ninja techniques, like his signature Rasengan. His experiences as a former underdog also shape how he trains his students, emphasizing perseverance and the power of friendship.
One possibility could be that Sakura is under Tsunade's tutelage while Naruto is trained by Jiraiya. This would lead to different styles of training. Sakura would focus more on medical ninjutsu and precise chakra control like Tsunade. Naruto, with Jiraiya, would learn more about summoning jutsu and unpredictable combat styles. Their growth paths would diverge in interesting ways, affecting how they interact with each other and their roles in the village.