In this fanfiction, a really interesting plot twist could be that the training by Shisui actually awakens a dormant power within Naruto that has nothing to do with the Sharingan at first glance. As Naruto delves deeper into the Sharingan training, he starts to notice connections between this new power and the Sharingan. Maybe it's a power related to the Sage of Six Paths that gets activated in a unique way due to the Sharingan training. Also, the relationship between Naruto and Shisui could take an unexpected turn. Instead of just a teacher - student relationship, they could become something like comrades with a shared mission that is revealed during the training process.
Naruto's character would likely become more serious and focused. Training with Shisui and the Sharingan would demand a lot of concentration, so he'd have to tone down his wilder side. He might also become more strategic in combat, as the Sharingan gives insights into opponents' moves.
In fanfiction, Shisui's Sharingan often has some unique abilities. It's usually depicted as having powerful genjutsu - related powers. For example, it might be able to cast illusions on multiple opponents at once with greater ease compared to a normal Sharingan. His Sharingan can also potentially be used to transfer memories in more creative ways in fan stories, like not just the basic memory transfer we saw in the original Naruto series but perhaps more complex emotional and skill - based memories.
The Akatsuki could still be the main antagonists. Since Naruto is being trained by Shisui, they would see Naruto as an even greater threat. His new skills under Shisui's training could put their plans at risk. For example, if Naruto becomes better at stealth and infiltration, he could disrupt their operations more effectively.
One possible plot could be that Shisui imparts his unique Sharingan - related skills to Naruto. For example, he might teach Naruto how to predict opponents' moves better, just like how the Sharingan can analyze the flow of chakra and movements. This would give Naruto an edge in battles, especially against strong opponents who rely on speed and deception.
In some fanfictions, Shisui's Sharingan has a different color or pattern. This is a simple but effective way to make it stand out. For example, it could be a deeper red or have an extra swirl in the pattern.
In a fanfiction where Naruto is trained by Shisui, it could change Naruto's whole ninja approach. Shisui was a very intelligent and skilled ninja. He could introduce Naruto to new forms of chakra control. This new training could make Naruto a more versatile fighter. For example, he might be able to combine his existing Rasengan techniques with the skills learned from Shisui, creating more powerful and unpredictable attacks. And Naruto's understanding of the ninja world and its politics might also be deepened through Shisui's teachings.
Well, it could be that Naruto, being neglected in the village, is noticed by Shisui. Shisui sees Naruto's potential and decides to train him in stealth and combat skills. Naruto then starts to grow stronger under Shisui's guidance, and eventually surprises everyone in the village with his newfound abilities.
Well, if Naruto gets Shisui's Sharingan in a fanfiction, he could gain some really cool abilities. The Sharingan has powers like enhanced perception and the ability to copy jutsu. Naruto already has his own powerful chakra and skills, so with the Sharingan, he might become an even more formidable ninja. He could potentially use the Sharingan's genjutsu capabilities to his advantage in battles, maybe even use it to break through tough enemy defenses more easily.
It could be some of the villagers who are jealous of Naruto's sudden growth under Shisui's training. They might try to undermine him or spread false rumors about him.