The plot might revolve around Naruto having to overcome some internal struggles while being trained by the Kyuubi. Since the Kyuubi is a force of nature, it has a different mindset from humans. Naruto would have to learn to balance his own values with the Kyuubi's more primal and power - hungry instincts. This internal conflict could lead to some interesting character development, such as Naruto becoming more assertive in battle and in his relationships with others.
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.
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, 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.
Well, it could be that DIO imparts his unorthodox and powerful combat skills to Naruto. Maybe Naruto learns DIO's time - stopping ability in some unique way, which gives him an edge in battles against tough opponents in the Naruto universe. And he might also pick up DIO's menacing charisma, making him a more intimidating presence on the battlefield.
In a 'Naruto trained by ANBU' fanfic, the plot could involve Naruto being secretly taken under the wing of ANBU members. They might train him in stealth and more lethal forms of combat. This could lead to Naruto having a different fighting style compared to canon, and he might face different challenges as he grows stronger. For example, he could be involved in more covert missions early on and develop a reputation among the ANBU ranks.
Well, it could start with Naruto being sent on a special mission where he encounters Sasori. Sasori, seeing potential in Naruto, decides to train him. The training would likely be tough as Sasori is a strict teacher. Naruto would have to adapt to Sasori's methods. He might learn how to control multiple puppets at once, and this new skill could help him in battles against stronger opponents in the future. For example, when facing Akatsuki members or other powerful foes.
In a fanfic where Naruto is trained by Zetsu, the story could take an interesting turn. Zetsu has knowledge of the Akatsuki and their secrets. Naruto could learn about the organization from the inside out. This knowledge could help him in his quest to bring peace. He might also gain some physical enhancements. Zetsu is quite durable in his own way, and Naruto could inherit some of that sturdiness. This would make him an even more formidable opponent in battles against strong foes like Pain or Madara.
Well, it could be that Itachi trains Naruto to better control his chakra. Maybe Itachi sees potential in Naruto to bring peace to the ninja world and decides to pass on his unique skills like the Sharingan's insights on combat.
In a 'naruto trained by ruby' fanfic, perhaps Ruby could introduce Naruto to some unique combat styles. Maybe Ruby has her own set of skills like some kind of magic or special weapon techniques. She could teach Naruto how to combine his chakra with these new elements. For example, if Ruby has some sort of elemental magic, Naruto could learn to infuse his Rasengan with that magic for a more powerful attack.
A 'naruto trained by orochimaru fanfic' might have Naruto delving deeper into the secrets of the Sharingan. Orochimaru has always been interested in the Uchiha's power. So Naruto, under his training, could be exposed to knowledge about the Sharingan and its potential. This might lead to some interesting power - ups for Naruto, but also put him in the crosshairs of other powerful ninja who are also interested in the Sharingan's secrets.
In a 'naruto trained by selphe fanfic', perhaps Selphe comes from a different ninja clan with ancient techniques. She could teach Naruto how to combine his existing Rasengan technique with her clan's special chakra manipulation. This would make Naruto's attacks even more powerful and unpredictable. Also, Selphe might train Naruto in mental discipline, which would help him better handle the stress of battles and his role as a future Hokage.