If Kurenai became Naruto's sensei in fanfiction, Naruto might learn some unique jutsu related to genjutsu. Kurenai is a genjutsu expert, and she could potentially teach Naruto how to use genjutsu more effectively or even develop his own genjutsu - based attacks. This could add a whole new dimension to Naruto's fighting style.
Well, perhaps in the fanfiction, Naruto being Kurenai's sensei could lead to him teaching her some unorthodox methods. Since Naruto has his own way of doing things, he might introduce her to new ways of fighting or thinking that completely revolutionize her ninja skills. This could create interesting storylines where Kurenai has to adapt to Naruto's teaching style while still holding on to her own values.
Their relationship could start off rocky as Kurenai might be hesitant to accept Naruto as her sensei. After all, Naruto is younger and has a very different style. But as time goes on, she would start to see the value in his teachings.
Kurenai's teaching style as Naruto's sensei would likely be more focused on genjutsu compared to Kakashi. Kakashi was more about overall combat skills and strategy. Kurenai would probably drill Naruto in the subtleties of genjutsu, like how to create more complex illusions and how to break through an opponent's genjutsu faster.
Tenten could be one of the characters. She could be Naruto's friend and also have a bit of a crush on him. Ino might also be present, using her mind - related jutsu to try and understand the complex relationships in the harem. Rock Lee could show up too, providing some comical relief and also being Naruto's loyal friend in the midst of all the relationship chaos.
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.
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.
I'm not entirely sure if there is a specific 'Naruto cheated on by Kurenai' fanfiction. Fanfiction websites are full of a huge variety of stories, and it could be quite difficult to find one with such a specific plot. You could try searching on popular fanfiction platforms like FanFiction.net or Archive of Our Own using relevant keywords, but keep in mind that the Naruto fandom has a wide range of story themes, and this might be a rather unusual one.
One aspect to consider in this fanfiction scenario is how their marriage would affect the other characters. The young ninja in the village might look up to them as a couple. Naruto's friends like Sakura and Sasuke would have different reactions. Sakura might be happy for Naruto but also a bit envious, while Sasuke might initially be skeptical but come to respect their relationship over time. And their family life could involve Naruto teaching their future children his unique ninja skills, while Kurenai imparts her wisdom about the more subtle aspects of being a ninja.