One common theme is redemption. Since Kakashi can go back in time, he often tries to make up for past mistakes or prevent tragedies that occurred in the original timeline. For example, he might try to save a character who died before. Another theme is the changing of fates. He can change the destiny of not only himself but also of his friends and the whole village. He can use his knowledge of future events to better prepare for threats.
One possibility is that there would be a lot of reminiscing. Team Minato was Kakashi's old team. They might talk about old missions, like the one where they faced the Stone ninjas. Kakashi could share how their teachings influenced his leadership as Hokage.
Emotionally, it would be a powerful encounter. They might share their feelings about the losses they've all faced, like the death of Minato. This could strengthen their relationships and also give Kakashi new insights as Hokage on how to protect the village better.
A cool plot would be Kakashi traveling back to a time during one of the great ninja wars, say the Third Great Ninja War. He could use his knowledge of future jutsu and strategies to turn the tides of battles that were previously lost. He might also be able to save comrades who died in the original timeline, and in the process, change the future of many ninja families.
One great Kakashi Hokage time travel fanfiction is 'Kakashi's Time - Travel Redemption'. In this fic, Kakashi goes back in time and uses his knowledge to prevent some of the tragedies that happened in the original timeline. He focuses on training the younger generation earlier and making strategic changes. It's a really interesting read as it shows a different side of Kakashi's leadership and how he could have changed the course of the Naruto world if given the chance to go back.
If Kakashi travels back in time, his actions could have a butterfly effect. For example, if he saves someone who was supposed to die, that person's actions in the future could be completely different. This could lead to changes in alliances, battles, and even the political structure of the village.
Perhaps a perk is the ability to shape the future of the ninja world. As Hokage, one can inspire the younger generation of ninjas. They can create new ninja academies or training programs. They also have the power to pardon or punish ninjas according to their deeds, which helps in maintaining law and order in the village.
Sasuke could also be a possibility for the 6th Hokage in the fanfic. He has grown stronger over the years and his unique perspective on the ninja world could bring new ideas to the leadership of the Hidden Leaf. He might start off as a controversial choice but prove himself through his actions in protecting the village and making tough decisions.
Sasuke could be an alternative. He has strong ninja skills and a deep understanding of the ninja world. His experiences have made him grow into a very capable person, and his Sharingan gives him an edge in combat and strategic planning.