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.
Naruto might be initially shocked and heartbroken. He has always considered the village his home, despite how some of the villagers have treated him. So being banished would be a huge blow to him.
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.
In a fanfic where Danzo gives Naruto the Sharingan, it could lead to a very different Naruto. Naruto might gain new abilities and a new perspective on the Uchiha. He could potentially master the Sharingan quickly with his strong willpower, but he would also have to deal with the dark side of the Sharingan, like the curse of hatred that often comes with it.
One possible motive could be revenge. Maybe the oc or someone close to the oc has been wronged by Danzo in the past. So, to seek justice, the oc decides to take him down.
Well, it really depends on how the fanfic is written. If the fanfic focuses on Naruto's weaknesses and Danzo's preparedness, Danzo could potentially win. He has a lot of political power and experience. However, if it follows the general power scale of the Naruto universe, Naruto has a better chance. His positive energy and the power of friendship (a bit cheesy but true in Naruto's world) often help him overcome his opponents. Naruto also has the ability to quickly adapt to new situations, which would be a big plus against Danzo.
A plot where Danzo fakes his death and teams up with Naruto undercover to take down a hidden threat to the village. They have to keep their alliance a secret from everyone, including the other village leaders. This creates a lot of tension and secrecy in the story.
Well, in such a fanfic, Naruto might turn against his friends. He could be made to use his power for Danzo's often shady purposes. For example, he might be forced to target those Danzo sees as threats to Konoha in a more brutal way than he normally would. His relationships would be severely damaged as his friends would be confused and likely try to stop him, not realizing he's been brainwashed at first.
The plot could involve Naruto having a philosophical discussion with Danzo. Naruto, with his idealistic views of peace and friendship, might try to sway Danzo from his more ruthless ways. They could talk about power, sacrifice, and what it really means to be a shinobi. Naruto could also demand answers from Danzo about the secrets he's been hiding from the village.
One idea could be a fanfic where Danzo actually manages to become Hokage through some underhanded means. Then Naruto has to find a way to expose his true nature and restore the rightful leadership to the village. Maybe he teams up with some of the other shinobi who were also suspicious of Danzo's actions all along.