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.
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.
One idea could be a story where a non - Uchiha character somehow gains the Sharingan. Maybe through a scientific experiment gone wrong in Orochimaru's lair. They then have to learn to control it without any prior knowledge of the Uchiha clan's ways.
Well, one idea could be exploring a scenario where Sasuke's Sharingan is overlooked by the village in a different way than in the original story. Maybe they see it as more of a curse than a power and try to suppress it, which could lead to a whole new set of conflicts for Sasuke.
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.
One idea could be a character from RWBY obtaining the Sharingan and using its abilities in combat. For example, Ruby could get the Sharingan and combine its precognitive abilities with her own speed, making her an even more formidable fighter.
One idea could be exploring a different origin for the Mangekyou Sharingan. For example, what if it was related to an ancient Uchiha pact with a hidden spirit? Another could be a story where a non - Uchiha character somehow gains the ability to use the Mangekyou Sharingan and has to deal with the consequences. Or perhaps a fanfiction where the Mangekyou Sharingan has additional powers that are not shown in the original Naruto series, like the ability to time - travel.
One idea could be a story where the main character, who has the Eternal Sharingan, has to face a new and powerful enemy that can manipulate time. With the power of the Eternal Sharingan, the character has to find a way to break the enemy's time - based attacks and defenses. Another plot could revolve around a character with the Eternal Sharingan trying to uncover long - lost secrets of the Uchiha clan that are hidden deep within the Sharingan's powers. Maybe there are ancient jutsu or prophecies that only the Eternal Sharingan can unlock.
One idea could be a story where Naruto somehow gains the Golden Sharingan. He could use its unique powers to see through genjutsu more easily and also have enhanced perception in battle. For example, he might be able to predict his opponents' moves better. Another plot could involve Naruto using the Golden Sharingan to unlock a new form of his Rasengan, perhaps one with the ability to disrupt an enemy's chakra flow on a deeper level. Or, it could be a story where Naruto has to team up with a character who has knowledge of the Sharingan to fully understand and control the Golden Sharingan's powers.
One idea is that an enemy targets Kakashi's Sharingan and Naruto has to protect it. Along the way, Naruto learns more about the Sharingan's capabilities and how to use it against the enemy. This would be a great opportunity for Naruto to grow as a ninja and for their friendship to deepen.
One idea could be that Hatake Kakashi somehow transfers his Sharingan to Naruto in a dangerous mission. This would give Naruto new abilities and a whole new set of challenges to face. He'd have to learn to control the Sharingan quickly while also dealing with the enemies who might target him specifically for it.