Well, it could have the ability to time - travel. Imagine Naruto using it to go back in time to prevent some of the great tragedies in the Naruto world, like the Uchiha massacre. This would change the whole storyline in a very interesting way.
His relationship with Sasuke would be very different. Since the Sharingan is an Uchiha - related thing, Sasuke might be both jealous and intrigued. They could end up being rivals in a whole new sense, competing to see who can master their respective powers better.
Sakura could be an unexpected character to have the Sharingan. It would completely change her character dynamics. She could use it to enhance her medical ninjutsu, seeing the internal body structure more clearly. Also, she could become a more formidable fighter, using Sharingan - based genjutsu to her advantage.
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.
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.
Well, normal Naruto mainly relies on his chakra and the Nine - Tails' power. But Dark Naruto with Eternal Mangekyou Sharingan would have unique visual jutsu. He could use the Sharingan's genjutsu abilities on a much greater scale, perhaps even trapping entire villages in an illusion without them realizing.
Sakura's character would develop in terms of her combat skills. The Sharingan would allow her to analyze her opponents' moves more quickly and accurately. This would also boost her self - esteem as she would no longer be seen as just a support ninja. She would start to take on more dangerous missions and grow as a leader within her team. For example, she could use the Sharingan to see through genjutsu more easily during battles, which would give her an edge. Additionally, she might develop a new sense of pride in her abilities that was not there before, as she now has a unique power that few others possess.
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.
Well, in fanfiction, one way could be that some Kumo ninjas are given the Sharingan as a gift or a curse from an ancient being. They then start to form a special group within the village dedicated to understanding and mastering the Sharingan. This group would share their knowledge with others, and over time, the Sharingan becomes an important part of Kumo's ninja heritage, with its own set of training methods and traditions.