It would be very close. Kakashi would be like a father or an older brother to them. Naruto and Sasuke would respect and rely on him. They would probably have a more harmonious relationship with each other too, because Kakashi would be there to mediate any conflicts.
The fanfiction would likely show a different side of their development. Since Kakashi is a very experienced ninja, he could expose Naruto and Sasuke to different types of missions earlier. This would accelerate their growth not only in terms of combat skills but also in terms of understanding the ninja world. And with Kakashi as their adoptive father - figure, they would have a stronger emotional support system, which could potentially prevent some of the tragedies that happened in the original story.
Well, Kakashi's adoption would likely bring more stability to their lives. He could train them more intensively and offer better guidance. Naruto might finally feel like he has a proper family, which could boost his self - confidence. Sasuke, on the other hand, could find a new sense of belonging and might be less likely to go down the dark path he did in the original story.
A fanfiction where they all go on a mission together in a strange, uncharted land. Kakashi is the leader as usual. Sasuke could struggle with his inner demons during the mission, Naruto would be trying to keep everyone's spirits up, and Sakura would be using her medical skills to keep them all in top shape. There could be new enemies and challenges that they have to face together, forcing them to rely on each other more than ever.
One idea could be a time - travel fanfiction. Naruto, Sasuke, Sakura, and Kakashi are sent back in time to their early days at the academy. They have the knowledge of their future selves and use it to change some of the events that led to hardships in their lives. For example, Sasuke could prevent the Uchiha massacre with their combined help.
One common theme is friendship. Given their long - standing relationships in the original series, fanfictions often explore how Sasuke, Sakura, Naruto, and Kakashi's friendships evolve over new challenges. Another theme is power and growth. Fans like to write about how these characters continue to gain strength and wisdom.
Well, for starters, Kakashi has to deal with Naruto's hyperactive and sometimes reckless behavior. Naruto often acts without thinking, which could put him in danger. Sasuke, with his complex emotions and the burden of his clan's massacre, is also a handful. Kakashi needs to make Sasuke understand that revenge is not the only way forward. Additionally, Kakashi has to ensure that both Naruto and Sasuke get along well with each other. There could be rivalry between them, and Kakashi has to manage that in a way that doesn't harm their relationship or their growth as ninjas.
In this kind of fanfiction, perhaps Kakashi notices Sakura's potential that is being overlooked. He might start training her more intensively, leading to Sakura developing new jutsu skills. For example, Kakashi could teach her some of his own special techniques, like his lightning - style jutsu in a modified form suitable for Sakura.
A plotline could be that there is a powerful new enemy that specifically targets their bonds. This enemy uses illusions and mind - control to try and turn Sasuke against Naruto, or make Sakura distrust Kakashi. They have to fight not only the physical attacks of this enemy but also the mental and emotional turmoil it causes within their group. In the end, they realize the true strength of their relationships and are able to defeat the enemy.