In the Naruto universe, while it's highly unlikely in the official canon, in fanfiction, anything can be made possible. The Sharingan is a kekkei genkai exclusive to the Uchiha clan. Danzo had Sharingan in his arm which he obtained through rather unethical means. For Naruto to get it from him in fanfiction, it could be written through some sort of experimental jutsu gone wrong or right. Maybe a jutsu that was meant to transfer power ended up giving Naruto the Sharingan. However, this would completely change Naruto's power dynamics and character arc as the Sharingan comes with its own set of abilities like the ability to copy jutsu, predict movements, and use genjutsu.
He'll likely lose his power and influence in the village. Once Naruto reveals his secrets, the villagers won't trust him anymore. His actions might be put on trial, and he could be exiled from the village.
It could also be due to Naruto's outcast status in the village initially. Danzo might think that banishing Naruto would be an easy decision as Naruto doesn't have many supporters at first. He might believe that by getting rid of Naruto, he can maintain the status quo in the village and prevent any disruptions that Naruto's presence might cause in the future.
There would be several implications. Firstly, Naruto's training would take a new turn. He would need to learn how to control and use the Sharingan properly, which could be a difficult task considering his already existing training regime. Secondly, politically, it could cause a stir in the Hidden Leaf. The Sharingan is a symbol of the Uchiha clan, and Naruto getting it from Danzo (who had a controversial relationship with the Uchiha) could lead to various political debates. Thirdly, on a personal level, Naruto might experience new emotions and temptations that come with the Sharingan's power. He might have to struggle with the darker aspects of the Sharingan, such as the potential to be consumed by its power, just as some Uchiha did in the past.
Well, in some versions, Naruto might use his influence among the villagers. After Pain's attack, the village is in a state of rebuilding and re - evaluating. Naruto, being a hero, has the ears of the people. He could start by presenting evidence of Danzo's underhanded deals, like his connection to Orochimaru perhaps. Maybe he found some secret documents during the chaos that Pain caused, which link Danzo to unethical experiments or power - grabbing within the village.
One possible motive could be to gain control over Naruto's power. Since Naruto has the Nine - Tails within him, Danzo might want to use that power for his own political or military gains. He's always been power - hungry and sees Naruto as a tool to achieve his goals of making Konoha stronger in his own way, which might involve more underhanded and controlling methods.
It could also be a completely new character introduced into the fanfiction. A foreign ninja who was inspired by some of Danzo's ideas (not the bad ones) and comes to Konoha to take on the role of successor, bringing in new perspectives and ways of doing things.
One way could be through the power of his friends. Their memories and the bonds he has with them might be strong enough to break through. For example, Sasuke's presence could stir something in Naruto, making him question the false beliefs Danzo has implanted in his mind.
There's a fanfic where Danzo tries to manipulate Naruto for his own political gain. However, Naruto, being the perceptive character he is, quickly catches on. This leads to a battle of wits between them. In the end, Naruto uses his own brand of talk - no - jutsu to make Danzo see the error of his ways and they end up working together to reform the village's political system.
One way Naruto could be like Danzo in fanfiction is through their view on secrecy. Danzo was big on keeping secrets and operating in the shadows. A fanfic could write Naruto into a scenario where he has to keep important information from his friends, believing it's for their protection, much like Danzo did. This would be a huge departure from his normal open and honest self.