In a fanfiction where Naruto gains One for All, there are a lot of possibilities. One for All gives the user enhanced strength, speed, and durability. Naruto already has a great deal of experience in combat and a strong will. This new power would allow him to face stronger opponents with ease. For example, he could take on the Akatsuki members more easily. Also, the way he trains and how he passes on his knowledge to others might change. He could potentially teach his friends how to better utilize their own powers in relation to One for All's abilities. His relationship with Sasuke might also be affected as they would have to re - evaluate their power levels in comparison to each other.
If Naruto gains One for All in fanfiction, his character would evolve in multiple ways. Firstly, his self - image would change. He's always been the underdog, but with this new power, he'd be on a whole new level. This could make him more empathetic towards those who are still struggling to find their strength. Secondly, his leadership skills would improve. He'd be able to inspire others not just with his words but also with his newfound power. His journey to master One for All would be filled with challenges, and through these, he'd become wiser. He'd also have to deal with the fact that this power is foreign to his ninja world, which would require him to be more adaptable and open - minded. All in all, Naruto's character would grow into a more complex and powerful individual.
Madara Uchiha could also be an antagonist in this scenario. Even if he's dead in the original story, in the fanfiction, his influence or some sort of resurrection could occur. He might view Naruto's immortality as a hindrance to his own plans for the ninja world or simply be jealous of Naruto having such a power that he never had.
Naruto might get a Zanpakuto that complements his existing powers. Since he has a strong connection to wind chakra, it could be a Zanpakuto with wind - based abilities. Maybe it could create powerful tornadoes or slices of wind that are sharper than his normal Rasengan - infused attacks.
With the Rinnegan, Naruto might gain the power of the Human Path. This would allow him to read minds or rip out souls, which is a very dark and powerful ability that would be quite different from his usual positive - natured powers.
If Naruto gains the power of Beerus in fanfiction, he would become extremely powerful. His already impressive combat skills combined with Beerus' god - like power would make him nearly unbeatable. He could easily defeat the toughest of foes in the Naruto universe with a single blow.
If Naruto gains the abilities of Kratos in fanfiction, he would become extremely powerful. Naruto already has his own set of powerful jutsu, but with Kratos' abilities like superhuman strength, enhanced combat skills, and his rage - fueled power, Naruto could defeat almost any enemy with ease. He might be able to take on stronger foes like Kaguya even more effortlessly and protect the Hidden Leaf Village in a much more dominant way.
One interesting plot could be that Naruto discovers a hidden ancient jutsu during a solo mission in an uncharted land. This jutsu gives him the power to manipulate time on a small scale, like slowing down an enemy's attack. Another plot might involve Naruto making a pact with a powerful spirit that grants him enhanced strength and the ability to fly. There could also be a plot where Naruto is exposed to a strange energy source that unlocks a new form of chakra, which he then has to learn to control and use effectively against his enemies.
If Naruto got the Rinnegan in fanfiction, he would become even more OP (over - powered). His fighting style would be completely different. He could use the Preta Path to absorb chakra attacks, which means he could nullify a lot of his opponents' moves. This would make him a much more formidable foe. In terms of the plot, it might lead to new alliances and rivalries. Maybe some characters who were previously neutral would now see Naruto as a threat, while others would flock to his side to benefit from his new power.
Another plot could be that Naruto is given immortality as a reward for saving the ninja world. The Sage of Six Paths or some other powerful entity decides that Naruto's selfless deeds deserve such a gift. So, he bestows upon Naruto the power of immortality, which then changes Naruto's perspective on life and his role in the ninja world.