Other characters like Sakura might be involved as well. She could be curious about how Naruto got the Sharingan and how it changes his abilities. Characters from the Uchiha clan, even if they are just mentioned in flashbacks, could be important. For example, Itachi's actions and the secrets he held about the Sharingan could be explored more deeply in relation to Naruto now having this power. And then there are the villains. They might see Naruto with the Sharingan as a new and greater threat or as an opportunity to gain power for themselves.
In many Naruto fanfictions, Itachi is often depicted as an extremely powerful Mangekyou Sharingan user. His original abilities in the canon, like Amaterasu, are further enhanced in fan works. Sasuke is also a common focus. His Mangekyou Sharingan's powers can vary greatly from one fanfiction to another, sometimes with new and unique jutsu created by the authors. Another character could be Madara. Fanfiction writers love to explore the full potential of his Mangekyou Sharingan, often giving him abilities that were only hinted at in the original series.
It could be Sasuke. Since he has the Sharingan, in fanfiction about the Eternal Sharingan, he might be a central figure, evolving his powers further.
Another common type of main character is a reincarnation of an ancient Sharingan user. In one fanfiction, Rei is a reincarnation of a long - dead Sharingan master. Her Sharingan has the power to see the future, and she uses this to try and prevent a great war from breaking out in the Naruto world. She teams up with Naruto and Sasuke in this story.
There could also be original characters created specifically for this fanfic. These new characters might have their own motives related to the Sharingan. For example, a new character could be a researcher who is trying to unlock the ultimate power of the Sharingan and sees Naruto as a key subject. They could add a whole new dynamic to the story.
A new character could be introduced as a Sharingan master. For example, a wandering ninja who has been secretly studying the Sharingan for years. He might have no allegiance to any village and travels around, looking for worthy pupils to inherit his knowledge. He could have unique techniques related to the Sharingan that no one has seen before.
Often, Naruto himself might be a main character in such fanfiction. He could be given the blue Sharingan through some strange event and then has to learn to use it. Another common character could be Sasuke. He might be involved in a plot where he discovers someone else with the blue Sharingan and either tries to help them or sees them as a threat.
Sometimes Naruto can also be a main character in these fanfictions. He might be the one who notices the neglect of Sasuke's Sharingan and tries to help him in some way. Their friendship could be explored in a new light, with Naruto being more proactive in understanding and supporting Sasuke's power.
Often, an original character created by the fanfiction author is the main character. This character might be an outcast ninja with the gray Sharingan who is trying to prove themselves in the ninja world.
In some cases, the 'naruto master of the sharingan fanfiction' could be about Naruto using the Sharingan to uncover secrets about the Uchiha clan that were previously unknown. This could tie into the overarching Naruto story, such as revealing more about the history of the Uchiha massacre or the true nature of the Sharingan's origin. It may also bring new story arcs where Naruto has to deal with ancient threats that were once related to the Uchiha and their powerful eyes.
There could be a young and ambitious ninja as the main character in 'naruto sharingan god fanfic'. This ninja starts out as an underdog but with the discovery of the Sharingan God, their life changes completely. There might also be a mentor - like figure, perhaps an old and wise ninja who has some knowledge about the Sharingan God and helps the main character on their journey. Additionally, there could be antagonists, like other power - hungry ninjas who want the Sharingan God power for themselves.