It could be Sasuke. In many Naruto - related stories, Sasuke has the Sharingan and is often the target of others' tricks or manipulations due to his complex personality and his power.
Maybe by creating false visual illusions. For example, using some basic ninja techniques like the Transformation Jutsu to disguise as someone important to the Sharingan user. This could make the Sharingan user misjudge the situation and fall into the trap.
Itachi, even though he is a very skilled Sharingan user. Naruto might come up with a clever plan to fool him. Maybe Naruto could use his understanding of Itachi's past and his relationship with Sasuke to create a situation where Itachi misinterprets what's going on. Also, other Uchiha clan members who rely heavily on the Sharingan could be victims. Naruto could study their common traits and weaknesses related to the Sharingan and use that knowledge to deceive them.
One possibility is that Naruto uses his wits and unique skills to deceive those who overly rely on the Sharingan. Maybe he creates false scenarios or uses his own abilities in a way that misleads Sharingan users into making wrong judgments.
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.
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.