Perhaps in the fanfiction, Kakashi is on the verge of losing his Sharingan due to an injury or curse. In a selfless act, he transfers it to Naruto. Naruto, being the determined and quick - learner he is, starts to explore the Sharingan's powers. He could use it to better understand his enemies' strategies during the Fourth Shinobi World War. The Sharingan could also create an interesting dynamic with his existing relationships, as his friends might be both amazed and a bit worried about this new addition to his powers.
One possible storyline could be that Naruto receives Kakashi's Sharingan through some sort of magical or experimental transfer. This new power could make Naruto even more formidable in battle. He might start to see the world in a different way, with the Sharingan's abilities to copy jutsu and predict movements. This could lead to new training regimens as he tries to master the Sharingan's full potential while still relying on his own Uzumaki powers like the Nine - Tails chakra.
The story might progress as Naruto struggles to control the Sharingan at first. He may have some internal conflict as he tries to incorporate this new power into his existing set of skills. As he gets better at using it, he could start to change the power structure in the ninja world. His relationships with his friends and allies could also be affected. For instance, Sakura might be more worried about him as the Sharingan could put a strain on his body. Naruto could also use the Sharingan to uncover secrets about his parents or the history of the ninja clans that were previously unknown.
One great fanfiction could be about Kakashi using his Sharingan to train Naruto in a special jutsu. Maybe he shows Naruto how to better perceive an opponent's moves by using the Sharingan's ability to analyze. This could lead to Naruto developing a new and powerful technique that combines his own chakra control with the insights from the Sharingan.
One possible storyline could be that Naruto's sister is also a ninja. She might be secretly trained by someone in the village, like an old hermit. And she could be very powerful, having a unique jutsu that even Naruto is amazed by. Maybe she has to hide her identity at first to protect Naruto from some unknown threats in the ninja world.
One possible reason could be that Kakashi is in a life - threatening situation and realizes that Naruto is the best candidate to inherit his Sharingan. He knows Naruto's potential and his desire to protect the village. Another reason could be that Kakashi wants to see how Naruto would use the Sharingan in combination with his own unique abilities. He's curious about the new powers and techniques that Naruto could create with it. Also, it could be a way for Kakashi to show his complete trust in Naruto, as the Sharingan is a very precious and powerful gift.
One possible storyline could be that Naruto somehow gains a Hyuuga eye through a unique experiment gone wrong. This new power could initially be difficult for him to control, as the Hyuuga eye has its own set of abilities like the Byakugan. He might struggle to adapt to the sudden change in his vision and the new skills it brings, such as seeing the chakra points clearly. This could lead to some comical moments as he accidentally activates the eye at inappropriate times, but also some intense battles where he slowly learns to master this new power and use it in combination with his existing Rasengan and other techniques.
One possible storyline could be that his older sister was sent away on a secret mission when Naruto was young. Years later, she returns, having gained great power and knowledge. She then helps Naruto in his journey to become Hokage, teaching him advanced jutsu and giving him emotional support during tough times.
The story could also involve Naruto's Pokemon bloodline being the key to solving a great mystery in the ninja world. His newfound abilities might attract the attention of both friends and foes. Some might see it as a great power to be harnessed, while others might fear it. Naruto would then have to navigate through this new situation, trying to understand his powers and use them for the good of his village, all while dealing with the politics and rivalries that come with having such a unique bloodline.
One possible storyline could be that Naruto's new 'four eyes' are a result of some strange jutsu gone wrong. Maybe he was trying to enhance his perception skills and ended up with an extra pair of eyes. These eyes could give him unique abilities, like seeing different types of chakra more clearly or even predicting an opponent's moves better. He might struggle at first to control this new change and it could be a source of both humor and growth in the story.
One interesting storyline could be Naruto discovers he has Sharingan after a strange encounter with an ancient Uchiha artifact. This new power makes his enemies question his identity and alliances, and he has to struggle with the newfound power while still being true to his ninja way.
Perhaps in the fanfiction, Kakashi is influenced by a dark power. This power corrupts his mind and makes him turn on Naruto. It could be related to some ancient curse or a new enemy's ability that targets Kakashi's mental state. Naruto, being the target, would then be at the mercy of Kakashi's attacks, creating a lot of drama and conflict in the story.