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.
One possible plot twist could be that Danzo is actually being controlled by an even greater enemy. So, when Naruto is about to defeat him, he realizes that there's a bigger threat behind Danzo. Another could be that Danzo reveals a hidden power that he has been suppressing all along and suddenly becomes much stronger than Naruto expected.
Minato might also be a prominent character. As their teacher, he can influence the way Obito and Kakashi interact. In some fan fictions, he could be the one to help them resolve their differences or provide some crucial information about their past that changes their current situation.
Some fanfictions might explore the emotional aspect of their fight. For example, how their past friendship affects the battle. Maybe Kakashi hesitates to strike a fatal blow because of their shared history.
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.
In some fan fictions, there might be a plot where Obito has a change of heart before a major battle with Kakashi. He could start to question his motives and the path he has chosen, leading to a very intense and emotional confrontation with Kakashi that is more about ideology than pure combat.
You could also check out Naruto fanfiction groups on social media platforms like Facebook. There are often enthusiasts who share and discuss their favorite fanfictions. Just search for relevant groups, join them, and then look for fanfictions about Kakashi vs Obito.
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 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.