How would Naruto's character develop in a fanfiction where he is trained by Kurama before the academy?
Naruto would be more confident. In the original, he was often bullied and looked down upon. But with Kurama's training, he would have a sense of self - worth and power early on. He might not be as loud and boisterous, as he now has real strength to back him up.
His ninja skills would be far more advanced for his age. He could have a better understanding of chakra manipulation and combat techniques. This would likely make him a bit of an enigma to the villagers and his future classmates at the academy. He might be more reserved as he doesn't want to reveal too much of what Kurama has taught him. His relationships would also be different. Instead of seeking approval desperately, he would be more focused on his own growth and how to use his new - found skills to protect the village.
Naruto's view of the world and his place in it would change significantly. With Kurama's training, he would realize that he has the potential to be a great ninja from a young age. This could lead to him having a more serious side. He would still be kind - hearted but not as naive. He would start to think about long - term goals like becoming Hokage in a more practical way. His relationship with Kurama would also be more of a partnership rather than just a host - tailed beast relationship. He would respect Kurama's wisdom and power and Kurama would see Naruto as a worthy pupil.