It could be Sasuke. Since the fanfic has 'Sharingan' in the title, Sasuke, who is well - known for his Sharingan abilities in the original Naruto series, might be one of the main characters.
Naruto might also be a main character in 'naruto ultimate sharingan fanfic'. Even though he doesn't have the Sharingan naturally, his connection with Sasuke and his role in the Naruto universe could make him an important part of the story. He could be involved in helping Sasuke develop or control his ultimate Sharingan powers.
It could be an evil ninja who also has a powerful form of the Sharingan. He might be jealous of Naruto's new ultimate Sharingan and wants to take it for himself. This antagonist could use his Sharingan powers to create illusions that are so powerful, even Naruto has a hard time breaking free from them.
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.
I'm not sure exactly as it's a fanfic, but likely there will be a character inspired by Naruto. There might also be characters related to the Sharingan's origin or those who are affected by the power of the 'holy' Sharingan.
Another possibility is that it could involve Naruto as a main character even though he doesn't have the Sharingan. His relationship with the character having the Eternal Sharingan could be explored. Maybe Naruto helps the character come to terms with their power or they team up to face a common enemy. This would add an interesting dynamic to the fanfic as Naruto's ideals and the power of the Eternal Sharingan collide and combine in different ways.
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.
The main characters in 'naruto the ultimate lover fanfic' could vary greatly. It might be a self - insert character created by the fanfic author who has an ultimate love for Naruto. Or it could be an original character who has a love story with Kakashi. Since it's a fanfic, the author has the freedom to create new relationships and characters, so it could really be anyone within the Naruto universe who is involved in this ultimate love scenario.
There might also be a mentor figure, someone who has taught the ultimate swordsman their skills. This character could be an old and wise ninja with a lot of experience in swordsmanship.
Most likely Naruto would be one of the main characters since it's a Naruto fanfic. He is usually the central figure in any Naruto - related story.
In this fanfic, perhaps there is a concept of the Sharingan evolving in ways that are completely different from what we know. It could be that the Sharingan has the ability to absorb not just jutsu, but also the life force of opponents, which would create a whole new dynamic in battles and power struggles within the Naruto universe.
One idea could be a story where the Sharingan evolves to an ultimate form that gives Naruto unique powers. For example, he might be able to use it to instantly teleport to any location he has previously visited. This would add a new dimension to his fighting abilities and his ability to save his friends quickly.