Well, perhaps they time travel to a period where a major ninja war was about to start. Fem Naruto, with her unique perspective, might try to find diplomatic solutions to prevent the war. Kakashi could be using his combat experience to train the ninjas of that time more effectively. Or maybe they go back to the time when Naruto's parents were alive, and fem Naruto gets to meet them and learn more about her heritage in a very different way than in the original story.
One plot idea could be that fem Naruto and Kakashi travel back to the founding of Konoha. They could use their modern - day knowledge and skills to influence the early development of the village in positive ways, like introducing new training methods. Another idea is that they travel to a time when a great enemy first emerged and they work to stop the threat before it becomes too powerful.
One interesting plot idea could be Kakashi traveling back in time to before the Uchiha massacre. He could try to prevent it, which would completely change the future of the Naruto world. Maybe he'd have to face off against Danzo and his schemes early on.
Perhaps in this fanfiction, Fem Naruto has a unique ability that only Kakashi can help her control. As they train together to master this power, they spend a lot of time in close proximity. This leads to them sharing personal stories and gradually falling in love. For example, Naruto might open up about her insecurities of being a female ninja in a male - dominated world, and Kakashi would comfort and encourage her.
One interesting plot idea could be that fem Naruto and Gaara travel back to the time when the Hidden Leaf Village was first founded. They could use their modern - day knowledge and skills to change certain events that had a negative impact on the village's future. For example, they might prevent a certain battle or reconcile feuding clans. Another idea is that they travel to a time when a great evil was about to be unleashed, and they have to work together to stop it before it's too late. Maybe they meet younger versions of their friends and family and have to convince them to trust their strange knowledge of future events.
One idea could be that fem Naruto travels back in time and has to hide her identity from Minato at first. She could then gradually reveal herself and use her future knowledge to help Minato prevent some of the tragedies that occurred in the original timeline. For example, she might know about certain Orochimaru plots and stop them before they start.
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.
Well, a cool plot might be Kakashi time - traveling to the era of the First Hokage. There, he could learn ancient jutsu and bring them back to his time. Maybe he gets involved in a conflict that was long forgotten but has implications for his present. He could also time travel during a crucial battle in his own past, like the fight against Obito, and change the outcome in unexpected ways.
Well, in some 'kakashi time travel fanfiction', Kakashi might travel back to change the fate of his village. He could go back to a time when there were internal conflicts in Konoha and resolve them before they escalated. Also, he could have the chance to reunite with his loved ones who had passed away, like his father. This would add a whole new layer of emotional depth to the story.
Perhaps a really cool plot twist is that the time travel was actually a trap set by an old enemy. When Kakashi and Naruto travel back, they find out that this enemy has been manipulating events from the past all along. They then have to not only fix the past but also figure out a way to stop this enemy from using the past to destroy their future.
They could time - travel during a great war in the past. Kakashi and Sakura might find themselves in the middle of battles they only read about in history books. They could use their modern - day skills to change the outcome of certain battles. This would also have a huge impact on the present - day Naruto world as they know it.
One idea could be that Sakura, as an Anbu, travels back in time and tries to prevent certain tragedies in Kakashi's past. Maybe she stops Obito from 'dying' initially, which would change the entire Naruto storyline in a major way.