He might gain enhanced perception abilities, which would be a huge boost to his combat skills. With the Sharingan, he could predict his opponents' moves more accurately.
It could cause some social unrest. The Sharingan is a symbol of the Uchiha clan, and Naruto having it might raise questions and suspicions among the ninja villages. Some might see it as a threat or an unnatural occurrence. Also, it would change his relationship with Sasuke, as they now both have a connection to the Sharingan in different ways.
One implication is that it changes his combat style. He can now use the Sharingan's abilities to predict enemy moves and copy jutsu more effectively. Another is that it might affect his relationships. For example, Sasuke might see him differently. Also, it could lead to new power - up scenarios and different training regimens in the fanfiction.
In fanfiction, if Naruto has the Sharingan, it can change his relationships. He might have a different connection with Sasuke, who is originally associated with the Sharingan. Also, it could lead to new story arcs. For example, he may need to learn how to control this new power, which could involve training with characters like Kakashi who also has the Sharingan. It can also attract the attention of different villains or groups who are interested in the power of the Sharingan.
It can also change Naruto's relationships. His friends might be in awe or even a bit scared of his new power. Enemies would surely target him more. Also, it could mean new story arcs. For example, he might have to deal with the dark side of the Rinne Sharingan's power, like being tempted by its overwhelming abilities. And he may need to find a way to use it for good without succumbing to its potential negative influences.
One implication is a change in his power level. The Mangekyou Sharingan gives access to powerful jutsus, so Naruto would be even more formidable. He might also face new enemies who are interested in his new ability.
If Naruto had the Sharingan in fanfiction, it would likely lead to some interesting power - up scenarios. He could combine the power of the Sharingan with his own massive chakra reserves. This might make him an even more formidable opponent. His training would also take a new turn as he'd have to learn to control and master the Sharingan's abilities, like the different levels of the Sharingan and their unique powers.
In fanfiction, Naruto getting Shisui's eye could lead to a whole new plotline. It could potentially be a way to bridge the gap between the Uchiha clan and Naruto. Since Shisui was an important Uchiha, having his eye might give Naruto a connection to the clan's history and secrets. This could play a role in resolving some of the long - standing issues between the Uchiha and the rest of the village. Naruto might also use the eye's powers in unique ways, like combining it with his own Uzumaki chakra, creating new and unexpected jutsu.
If Naruto had a Sharingan in fanfiction, it would drastically change the story. He could quickly copy enemy jutsus like Sasuke. His combat ability would skyrocket as he could predict movements better. Also, his relationships might change. For example, his bond with Sasuke could be different as they'd both have the Sharingan. It would also make his training with Kakashi more interesting as Kakashi could teach him unique Sharingan - related techniques.
One possible plot implication could be that Naruto gains some of Sasuke's abilities or perspectives. Since the Sharingan is a powerful and unique eye in the Naruto universe, Naruto might be able to see things in a different way. For example, he could better understand Sasuke's past actions or motives. Maybe he could also use some of the Sharingan's combat abilities, like predicting enemy movements more accurately, which would change the power dynamics in battles. This could also lead to some interesting character development as Naruto has to deal with these new powers and how they affect his relationships with others, especially Sasuke.
A rogue Uchiha who has lost the use of one of his Sharingan eyes due to a failed experiment. He becomes jealous of the protagonist who has one working Sharingan eye and tries to take it for himself. He might use his remaining Sharingan powers in cruel and unexpected ways to try and defeat the protagonist.
The Juubigan in fanfiction for Naruto often means a shift in the power balance. His relationships with other characters might change too. Allies could be in awe of his new power, while enemies would be more fearful. It also might open up new plotlines like Naruto having to learn to control this new power so as not to accidentally harm his friends.