In some fanfictions, it could be through a divine intervention by Kami. Maybe Kami sees Naruto's pure heart and his need for more power to protect the village. So, Kami decides to bestow upon Naruto the power of Madara's Sharingan as a way to give him an edge in battles against powerful foes.
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.
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 possible fanfiction could be about a young ninja who discovers he has a special connection to Madara's Sharingan. Maybe he inherits some of Madara's latent powers through a mysterious family link. This could lead to him being hunted by those who want to use his power for evil or by those who fear it.
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.
One way could be through a kekkei genkai transfer jutsu. If a powerful ninja, perhaps an old hermit with knowledge of ancient jutsus, decides to transfer Sasuke's Sharingan to Naruto for the greater good of the village. This jutsu might be risky but in the world of fanfiction, anything is possible.
Well, Naruto getting Madara's Sharingan in a fanfic would be wild. First off, the Sharingan could potentially enhance Naruto's combat awareness even more. He might be able to see through genjutsu easier, not just because of his own chakra but also the Sharingan's anti - genjutsu capabilities. Also, it could open up new story arcs where Naruto has to learn to control the Sharingan's powers, which are quite different from his normal ninja skills.
Naruto's character would experience a significant shift. He has always been known for his raw power and determination. With the Sharingan, he would gain a new level of perception. This could make him more cautious in battle as he now has the ability to see things in more detail. Emotionally, he might become more reserved as he tries to understand the Uchiha's history and the significance of the Sharingan. His growth would not only be in terms of power but also in his understanding of different ninja clans. He would strive to use the Sharingan in a way that unites the ninja world rather than divides it, showing his growth as a character who values peace and unity above all else.
The popularity of 'naruto madara sharingan fanfic' comes from the mystery surrounding Madara and his powerful Sharingan. Fans are always eager to explore more about it.
Yes, there are many. You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Naruto Eternal Sharingan Sasuke' and you'll find a bunch of them, but the quality may vary.