Well, in certain fanfiction concepts, there might be a situation where the chakra of Itachi and Naruto somehow merges. This could be due to a fight against a common, extremely powerful enemy. During this intense encounter, their chakra intermingles and as a result, Naruto ends up with Itachi's Sharingan. It's a really interesting concept that allows for new storylines and character developments in the fanfiction world.
In some fanfictions, it could be through a special jutsu or ritual. Maybe Itachi, before his death, transferred his Sharingan to Naruto in a unique way, perhaps using a forbidden technique that was known only to a few in the Uchiha clan.
He might have increased visual abilities. For example, he could see chakra flow more clearly, which would be a great advantage in battle.
One way could be through a powerful jutsu gone wrong. Maybe a jutsu that was meant to transfer Itachi's memories to Naruto accidentally transferred his Sharingan as well. In the world of fanfiction, there are often many creative and out - of - the - box explanations.
In some fan theories, it could be due to a unique chakra interaction. Maybe the Kyuubi's powerful chakra somehow mutates Naruto's own ocular abilities and triggers the emergence of the Sharingan. But this is just a wild fanfiction idea.
Naruto would gain the ability to copy jutsu. With the Sharingan, he could watch an opponent's movements closely and replicate their techniques. This would be a huge advantage for him in battles.
In some fanfictions, it could be due to a special jutsu gone wrong. Maybe a jutsu that Kakashi was using to transfer some of his chakra to Naruto for a mission accidentally transferred his Sharingan power as well.
They could develop a mentor - mentee relationship. Itachi uses his knowledge of the Sharingan to teach Naruto new combat techniques. As they train together, they bond over their shared experiences of loss and their desire to protect the people they care about. Naruto might also help Itachi come to terms with his past actions and find some peace within himself.
One possible fanfiction could be that Itachi, on his deathbed, decides to transfer his Sharingan to Naruto. He sees in Naruto the potential to change the Uchiha's fate and the ninja world. Naruto, with the Sharingan, gains new abilities like enhanced perception and the ability to copy some jutsus more easily. He uses this new power to better understand the Uchiha and bridge the gap between them and the rest of the village.
I really liked 'Itachi's Hidden Truths'. In this fanfic, the author gives a different perspective on Itachi's actions. It shows how his Sharingan abilities were not just for combat but also for protecting those he cared about in his own, often misunderstood, way.
Well, Naruto's abilities would change drastically. The Sharingan gives the user enhanced perception, which would make Naruto even more formidable in combat. He could potentially predict his opponents' moves better. Also, with the Sharingan's ability to copy jutsu, Naruto might be able to learn and use new techniques more quickly. However, he would also have to deal with the potential negative effects of the Sharingan, like overusing it and straining his eyes.
In fanfiction, it could be due to a strange encounter with a magical or ancient artifact. This artifact has the power to transfer the Sharingan's essence from Madara to Naruto. It might be a relic from an ancient battle between the Uchiha and some other powerful force, and when Naruto and Madara come into contact with it, the transfer occurs.