If Naruto had both in fanfiction, he'd be insanely powerful. His combat abilities would skyrocket. He could use the Sharingan to quickly analyze his opponents' moves and the Rinnegan to counter with powerful six - paths techniques. For example, he could use the Sharingan to predict an enemy's attack and then use the Rinnegan's Deva Path to repel it with ease.
Well, Naruto having the Mangekyou Sharingan and Rinnegan in fanfiction would change him a great deal. His character development would involve a lot of self - discovery. He'd be constantly exploring the limits of these powers, which would take him away from his home village more often. This would make him miss his friends and family, adding a new layer of emotion to his character. He'd also have to deal with the envy and fear of others who might see him as a threat because of his powerful eyes. But through it all, Naruto would strive to use these powers for the greater good, and this would shape him into a more mature and respected ninja in the fanfiction world.
If Naruto had the Sharingan and Rinnegan in fanfiction, his combat abilities would be off the charts. With the Sharingan, he could copy his opponents' jutsu much more effectively than before. And the Rinnegan would give him access to powerful abilities like the Six Paths Techniques. He might be able to control gravity, absorb and release chakra in new ways, and have enhanced perception of his surroundings.
Well, for starters, his power progression would be completely different. Without parental support, he'd have to figure out the Rinnegan's abilities all by himself. Maybe he'd accidentally unlock some dangerous powers early on because he didn't have anyone to guide him. His emotional state would also be a mess. He'd probably be angry at his parents for neglecting him and use that anger as fuel to train harder.
Naruto would become more introspective. The Mangekyou Sharingan often comes with a heavy burden and dark secrets. He'd have to deal with the new powers and the potential corruption they bring. For example, he might start to question his own motives more often.
In the wider ninja world, his relationship with other villages would change. Some villages might see him as an even greater threat now that he has the Rinnegan, and might try to form alliances against him. However, Naruto being Naruto, he would use his new power to show that he still has the same kind - hearted goals. He would try to use the Rinnegan to bring about peace even more strongly, and over time, win over those who were initially suspicious.
He might also become more isolated at first. The power of the Rinnegan could make him feel different from his friends. He may think that they can't understand what he's going through with this new power, so he could withdraw a bit until he learns to balance his new abilities with his old relationships.
If Naruto had both powers, his relationship with Sasuke would be affected. Sasuke might see Naruto as an even greater rival or, on the other hand, might be more willing to work with him. They could train together to better understand and control these new combined powers. Sakura might be in awe of Naruto's new abilities and try to support him in a different way, perhaps by researching more about the Sharingan and Rinnegan to help him. Kakashi, having knowledge of the Sharingan, could mentor Naruto in using it in combination with the Rinnegan.
If Naruto got the Rinnegan, he might become more cautious. The power of the Rinnegan is so great that he would realize he needs to be more careful with it. He wouldn't be as brash as before.
Well, it changes the story in many ways. Firstly, Naruto's power level would skyrocket. With the Rinnegan, he could use abilities like the Six Paths techniques. And the Sharingan would enhance his perception and give him new jutsu like Amaterasu or Tsukuyomi in theory. This would make him even more of a force to be reckoned with against foes like Madara or Kaguya. He could potentially end battles much quicker and might not need as much help from his friends as in the original story.
Naruto would probably become more of an outcast in some ways. Since the Sharingan is an Uchiha - specific power, having it as a non - Uchiha like Naruto would make others suspicious. This could make him more distrustful of others and more reliant on his own new powers. He might also become more strategic in his battles, using the Sharingan's abilities to analyze his opponents better.