Well, Kurama might train Naruto by teaching him how to better control and access chakra. Since Kurama has a vast amount of chakra, it could show Naruto unique ways to harness and use it. For example, it could guide Naruto in creating more powerful and complex jutsu by using their combined chakra in a more efficient way.
The outcome of the fight in the 'naruto fights the kyubi fanfiction' is quite uncertain. Naruto has his own set of skills, like his Rasengan and his ability to use shadow clones effectively. On the other hand, the Kyubi has raw power that is almost unrivaled. If Naruto is able to find a weakness in the Kyubi, perhaps something related to its past or its connection to the ninja world, he could win. But if the Kyubi manages to break Naruto's spirit, then the Kyubi would be the victor.
In this kind of fanfiction, Naruto might face a great challenge. He could use his new jutsu that he has learned over time to combat the Kyubi's powerful attacks. Maybe he'd have to tap into some hidden reserves of his chakra.
One great Naruto fanfic about him controlling Kyubi power is often centered around his growth as a ninja. It shows how he overcomes the initial struggle of harnessing such a powerful force within him. As he gradually gains more control, his abilities in combat and his standing in the ninja world improve significantly.
Another theme is acceptance. Naruto has to accept the female Kyuubi as she is, with her own personality and motives. And the female Kyuubi has to accept Naruto's way of life and his values. This mutual acceptance is often a key part of the story. For instance, in some fanfictions, the female Kyuubi initially doesn't understand Naruto's desire to protect the village, but gradually comes to accept it.
The Kurama Brothers could be entities that have a similar origin to Kurama. They might have been part of the same chakra - based creation in the Naruto universe. They could possess some of Kurama's traits like great power and a connection to the natural energy in the world. They are often depicted as having their own personalities, with one being more hot - headed and the other more calm and calculating. Their relationship with Naruto usually involves them using their powers and knowledge to help Naruto grow as a ninja and a person. They might also have their own goals and motives that are intertwined with Naruto's journey.
For Naruto, it would be a whole new experience. He'd be constantly trying to communicate with the mecha Kurama, learning its quirks. Shikamaru might be the one thinking about the strategic uses of mecha Kurama in battle. He'd be coming up with plans on how to best utilize it. As for Kurama, he could be in an internal struggle. Part of him would want to stay relevant in Naruto's battles, while another part would be curious about this new mechanical version of himself and how it could help Naruto in the long run.
You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own. Use the search function and type in 'Naruto' and 'Kyubi' to find relevant stories.
One possible plot twist could be that Naruto, while in his Kyubi form, loses control completely and starts to attack his friends. This would create a huge internal conflict for him when he comes back to his senses. Another could be that his transformation into the Kyubi gives him new abilities that are not related to just brute strength, like the power to communicate with other ancient beasts. Also, perhaps the transformation is not permanent, but rather fluctuates based on his emotions, leading to some really tense moments during battles or important interactions.
You can start by looking on fanfiction.net. It has a large collection of Naruto - related fanfics, and you're likely to find many 'naruto y kyubi fanfic' there.