Perhaps in the fanfiction, there is some kind of magic or special chakra that gets infused into Naruto. This foreign chakra could be related to the Sharingan's origin. It then triggers the activation within him. For example, if there is an ancient artifact that holds the essence of the Sharingan and Naruto comes into contact with it, it might start the process of activation.
I think Kakashi could also be an ally. Kakashi has a wealth of knowledge and experience, and he would be able to offer strategic advice to Naruto. Also, given his own Sharingan experiences, he might be able to help Naruto better understand and control the Rinnegan. Shikamaru is another possible ally. His intelligence and strategic thinking would be invaluable in helping Naruto make the best use of his Rinnegan powers in various situations, like in battles or in diplomatic negotiations within the ninja world.
Well, one possible plot could be that Naruto's Rinnegan gives him the ability to understand and communicate with all living things on a deeper level. So he can use this to broker peace between warring factions in the ninja world. He might be able to sense the true intentions of people and prevent conflicts before they start. It could also mean that he has a new understanding of chakra and how to use it in ways that were previously unknown, like combining different types of chakra in unique ways.
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 reason could be that some fanfiction authors might focus more on other aspects like new jutsu or character relationships outside of the Uchiha clan. They may not fully understand the potential of Sharingan, which has a wide range of abilities from basic perception enhancement to powerful genjutsu. Another factor could be the over - popularity of some other elements in the Naruto universe, like the tailed beasts, which overshadow the Sharingan in their stories.
Yes, in some fanfictions, Naruto can be depicted as having the Sharingan. Fanfiction writers often like to play with different character abilities and combinations, so it's not uncommon to see Naruto with the Sharingan in their creative works.
The Sharingan in such a fanfiction could be used as a tool for a Fairy Tail character to gain an edge in their battles. They might initially struggle to control it, but as they learn more about it, they become a formidable force. For instance, they could use the Sharingan's genjutsu abilities to deceive opponents in the Fairy Tail battles.
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.
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.