In fanfiction, Naruto could get the Sharingan through a blood - related connection that is revealed later. For example, it could be discovered that he has some distant Uchiha ancestry that gets activated somehow. Maybe a powerful enemy's attack awakens this dormant Uchiha blood in him, and as a result, he develops the Sharingan. It could also be that a powerful sage or a new character uses their own unique powers to bestow the Sharingan upon Naruto for a specific purpose.
A really cool plot idea is that Naruto's godlike Sharingan allows him to merge different ninja techniques. So he could combine a Rasengan with a Sharingan - based genjutsu. This would make him an even more formidable opponent. And it could also lead to some really creative battle scenes against strong enemies like Madara or Kaguya.
Naruto would likely become more confident. With such a powerful ability as the godlike Sharingan, he would know he has an edge in battles. He might also become more cautious, as he realizes the great responsibility that comes with such power. For example, he wouldn't want to accidentally harm his friends with a new, powerful genjutsu from the Sharingan.
If Naruto had the Sharingan in fanfiction, it would likely lead to some interesting power - up scenarios. He could combine the power of the Sharingan with his own massive chakra reserves. This might make him an even more formidable opponent. His training would also take a new turn as he'd have to learn to control and master the Sharingan's abilities, like the different levels of the Sharingan and their unique powers.
Naruto might adapt by first trying to understand the basic functions of the Sharingan. He could start with the simple ability to see chakra flow more clearly. Since he has always been perceptive about people's emotions, he could use the Sharingan to read the emotions of his enemies through their chakra, which would help him in battles.
One drawback could be the strain on his body. The Sharingan is a powerful dojutsu, and Naruto's body, which is used to his own chakra system, might not be able to handle it well at first. This could lead to fatigue and over - exertion during battles.
In this fanfiction concept, Naruto and Sasuke as brothers could lead to a very different Naruto universe. With Sasuke having the Sharingan, he could potentially use it to protect Naruto more often. Maybe they would train together in new ways, combining Sasuke's Sharingan - related jutsu with Naruto's Uzumaki power. For example, Sasuke could use his Sharingan to analyze Naruto's chakra flow and help him master new forms of the Rasengan faster.
Yes, in some fanfictions, Naruto is given the Sharingan. Fanfiction writers often like to play with the concepts and powers in the Naruto universe, and giving Naruto the Sharingan can lead to some really interesting storylines. It might be a result of some kind of power transfer or a unique plot device.
One possible fanfiction could be that Naruto is on a mission and encounters a powerful Uchiha who, instead of killing him, transfers his Sharingan to Naruto for some mysterious reason. Naruto then has to learn to control this new power while still maintaining his own unique ninja style.
One great fanfiction could be 'The Female Naruto's Sharingan Adventure'. In this story, the female Naruto discovers she has Sharingan abilities. It's a really interesting take as she has to learn to control this new power while still dealing with the normal Naruto - like challenges in the ninja world. She uses her Sharingan in unique ways during battles, which makes for some exciting fight scenes.