I think it's pretty far-fetched. The Rinnegan is not something Naruto would typically obtain, especially in a Narusaku context. It could make the story less believable and stray too far from the original canon.
His relationships would change too. Some of his friends might be a bit intimidated by his new power at first. But Naruto would work hard to show them that he's still the same person. He could also form new alliances with those who are interested in the Rinnegan's power, either for good or bad reasons. Overall, he would grow into a more complex and powerful version of himself, with a greater sense of responsibility for the ninja world.
Another possibility is that it's a result of some strange chakra experiment gone wrong (or right). Scientists in the Naruto universe are always dabbling in chakra research. Maybe an experiment meant to enhance her natural abilities instead gives her the Rinnegan, and she then has to learn to control it quickly to avoid being consumed by its power.
In many Narusaku fanfics, Naruto might bring Sasuke back through the power of their friendship. Naruto's unwavering belief in Sasuke could be a key factor. He may constantly remind Sasuke of their past together, the bonds they formed as teammates in Team 7. For example, Naruto could recall the times they trained together, their shared dreams, and how they protected each other in battles. This could slowly chip away at Sasuke's resolve to stay away and eventually lead him to come back.
You can find 'Naruto Shippuden Narusaku fanfic' on some popular fanfic websites like Fanfiction.net. There are a large number of Naruto - related fanfics on this site, and you can easily search for Narusaku ones. Another option is Archive of Our Own (AO3). It has a great collection of fanfics, and you can filter your search specifically for Narusaku fanfics within the Naruto Shippuden category.
You can try looking on fanfic websites such as FanFiction.net or Archive of Our Own (AO3). These platforms have a large collection of fanfictions, and there's a good chance you'll find 'narusaku naruto returns fanfic' there.
He could become more confident, bordering on overconfident at times. With the Rinnegan, he has access to incredible powers, and this newfound strength might make him believe that he can handle any situation alone. However, his friends would surely keep him in check. For example, he might initially rush into a battle thinking his Rinnegan - enhanced abilities will ensure victory without fully considering the risks, but then realize his mistake when his friends point it out.
Regarding the characters who possess the Rinnegan in the original and the fanfic, there are differences. In the original, we mainly see characters like Nagato and Sasuke with the Rinnegan. In the fanfic, new characters might be introduced with the perfect Rinnegan. These characters could have different relationships with other Naruto characters and different goals, which can significantly change the overall narrative compared to the original story.
When writing such a fanfic, start with a strong plot. For example, you could base it on a conflict. Say, an evil force is trying to take over both the Naruto and Fairy Tail worlds, and only by combining the powers of the Rinnegan and Fairy Tail magic can it be stopped. As for the writing style, use vivid descriptions to bring the battles and magic to life. Also, don't be afraid to introduce new characters that are a blend of the two universes, like a ninja - mage hybrid.
The way these eye powers are depicted can also vary depending on the plot of the fanfic. If the fanfic is about a character's growth, the acquisition of one of these eye powers could be a major turning point. For instance, a character getting the Rinnegan might start as a weakling but quickly become a powerful force to be reckoned with. Writers may also explore the psychological impact of having these powers, like how the Sharingan's ability to remember every detail could drive a character mad, or how the Byakugan's all - seeing nature could make a character feel isolated.
In fanfiction, the idea of Naruto having the Sharingan and Rinnegan is often a creative and out - of - the - box concept. It could be due to some kind of powerful jutsu or a unique plot device. Maybe a powerful enemy uses a forbidden jutsu that somehow transfers the powers to Naruto. Another possibility is that in an alternate universe created by the fanfic writer, the rules of chakra and kekkei genkai are different, allowing Naruto to possess these powers.