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.
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 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.
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.
In this kind of fanfiction, Naruto might obtain Shisui's brother's Sharingan through some unforeseen events. Maybe Shisui's brother sacrifices himself and entrusts his Sharingan to Naruto. As for new abilities, it could enhance Naruto's perception skills like being able to see through genjutsu more easily and also improve his combat awareness in battles.
One plot implication could be that Naruto becomes an outcast among some in the village who fear the power of the Sharingan. This would create internal conflict within Konoha. Another is that Naruto might be targeted by enemies who want to either steal the Sharingan or kill him to prevent him from becoming too powerful. Also, it could change his relationship with Sasuke, as they both now share a connection to the Sharingan.
One possibility is that Naruto would gain incredible new abilities. Shisui's Sharingan had unique powers like Kotoamatsukami. With it, Naruto might be able to influence others in a more subtle way. He could use it in battles to deceive opponents or even resolve conflicts without direct combat. For example, he could use it to make enemies see illusions of peace and lay down their weapons.