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, the concept can be very creative. It could be that Naruto has done some great deeds that caught Kami's attention. For example, Naruto might have saved a sacred place or creature related to Kami. As a reward, Kami decides to give Naruto Madara's Sharingan. This new power could then lead to many new storylines in the fanfiction, such as Naruto having to learn how to control this foreign power, and how it changes his relationships with other characters, especially those who are also related to the Sharingan like Sasuke.
It could have a huge impact on the balance of power in the ninja world. With Naruto having Madara's Sharingan, other villages might become more cautious or even hostile towards Konoha. This would lead to new political situations and alliances. Moreover, Naruto's training and growth would take a new direction. He would need to learn how to combine his existing abilities with the new powers of the Sharingan, which would be a complex and interesting process to explore in the fanfiction.
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.
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 fanfiction, if Naruto got the Sharingan from Madara, it would completely change his power dynamic. He would gain the abilities of the Sharingan like enhanced perception, the ability to copy jutsu more easily, and perhaps even access to some of Madara's unique Sharingan - based techniques. This would make him an even more formidable opponent and could potentially change the entire plot of the Naruto universe within the fanfiction world.
A fanfiction could focus on a character who is immune to the effects of Madara's Sharingan. This character could be a new type of ninja from a far - off land with a unique chakra nature that counteracts the Sharingan's genjutsu and other abilities. The story could be about how this character challenges Madara and changes the power dynamic in the Naruto universe.
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.
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.
In fanfiction, the 'kami' could be an original deity created by the author. This new 'kami' could have its own motives and reasons for giving a gift to Naruto. Maybe it's a kami that has been observing Naruto's journey and decides to interfere to help him achieve a greater purpose. It could be a kami associated with nature, like a kami of the wind or the fire, and the gift could be related to that element.
In some fanfictions, it could be through a strange and powerful jutsu transfer. Maybe Madara, on the verge of defeat, decides to transfer his Rinnegan power to Naruto for some unforeseen reason, like seeing a new path for the ninja world in Naruto.
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.