If Naruto is trained by Kyuubi in a fanfic, it would change a lot of things. Firstly, Naruto's relationship with the Kyuubi would shift from a more adversarial one (initially) to a mentor - student relationship. Kyuubi could train Naruto to use its chakra more efficiently, which would enhance Naruto's physical abilities like speed, strength, and endurance. Naruto might also gain a deeper understanding of the nature of chakra itself. Kyuubi could pass on some of its ancient knowledge about the ninja world, and this could help Naruto in his quest to protect the village and his friends. Moreover, Naruto's standing in the ninja world would rise even more as he becomes more powerful under Kyuubi's tutelage.
Well, it could be about Naruto learning unique combat techniques directly from the Kyuubi. The Kyuubi, being a powerful and ancient entity, might teach Naruto some forgotten or forbidden jutsu. This would set Naruto apart from his original training path in the canon series. Maybe he'd learn how to use the Kyuubi's chakra in a more controlled and strategic way, like creating chakra shields or new types of elemental attacks.
The Akatsuki could still be the main antagonists. Even with Naruto's training by the Kyuubi, they would be after the tailed beasts. Their goals of collecting all the tailed beasts would put them in direct conflict with Naruto. And they have some really powerful members like Pain and Itachi.
It could be an original character created by the fanfiction author. This character might be a descendant of the original Kyuubi, but with a female form and her own distinct personality.
His confidence would soar. With Kyuubi's training, Naruto would realize his true potential and become more self - assured. He'd be less likely to doubt himself in battles.
Naruto might become more in tune with the Kyuubi's power. He could access more of its chakra easily and use it more effectively in battle. For Hinata, she may gain a new sense of boldness. The training could make her less shy and more assertive in combat situations.
Well, in such a fanfiction, it might be that Naruto becomes extremely powerful like a god. Since he is trained by the Kyuubi, he could gain unique powers and abilities. Maybe he masters the Kyuubi's chakra in ways no one else has. He could use this power to defeat powerful enemies, protect his village in extraordinary ways, and perhaps change the entire shinobi world with his new - found god - like strength.
Yes, there are likely fanfictions with such a concept. The idea of a 'godlike' Naruto trained by the female Kyuubi is an interesting and popular concept in the Naruto fanfiction community. It allows for unique storylines and character developments.
The main character is Naruto without a doubt. He is the one on the path to becoming god - like through the Kyuubi's training. The Kyuubi is another key character. It has a vast amount of knowledge and power, and it imparts this to Naruto. Additionally, characters like Jiraiya could be important. Since Jiraiya was Naruto's mentor in the original story, he might play a role in this fanfiction too, perhaps guiding Naruto in a different way in combination with the Kyuubi's training. And then there are Naruto's friends. Sakura could be there to support Naruto or be in awe of his new powers. Sasuke might be an interesting character as he could be Naruto's rival, either trying to catch up to his power or oppose him if their paths diverge due to Naruto's god - like transformation.
The training by the fem Kyuubi could also change Naruto's view of the world. He might start to see the tailed beasts in a new light, not just as powerful and dangerous entities but as beings with their own personalities and stories. This could potentially lead to him trying to bridge the gap between humans and tailed beasts in the fanfiction world.