Maybe they travel back to a time when Tsunade was just starting to develop her medical ninjutsu. Naruto, with his understanding of modern medical knowledge (from Sakura perhaps), could help her make great leaps in her medical skills. They could also team up to deal with a powerful enemy that was a threat at that time. Naruto's strength combined with Tsunade's budding abilities would make for an exciting story.
A plot could involve young Tsunade being in a difficult situation where she loses confidence in her abilities. Naruto, who has always been about believing in oneself, comes across her and through his own experiences and words of encouragement, helps Tsunade regain her self - assurance and in turn, she helps him improve his ninjutsu control.
How about a story where Naruto is accidentally sent back in time and meets young Tsunade? At first, Tsunade is skeptical of Naruto, but as she sees his abilities and his kind heart, she starts to trust him. They end up teaming up to prevent a major disaster that was supposed to happen in the past. This not only saves the village in the past but also has unforeseen consequences for the future. Or a plot where young Tsunade is in a slump, and Naruto, with his infectious energy, tries to cheer her up. They end up exploring new parts of the village together, and in the process, they learn a lot about each other and themselves.
One idea could be a time - travel plot where Naruto is sent back in time and meets a young Tsunade. He could help her deal with the loss of her loved ones in a different way than she originally did, which in turn changes her future personality a bit. Another plot could be a mission - based story where they are paired up for a difficult task that only their combined skills can solve. For example, Naruto's Rasengan and Tsunade's super strength could be used to defeat a powerful enemy that requires both brute force and a tricky jutsu.
One idea could be Tsunade traveling back to the time when the Hidden Leaf was first founded. She could use her medical and combat skills to help the early settlers deal with diseases and threats from other villages. Another plot could be her going back to the time of the Third Great Ninja War and changing the fates of some of the fallen ninjas with her knowledge of future events.
One idea could be a story where Naruto gets seriously injured on a mission and Tsunade uses her medical skills to heal him. During the recovery process, they start to develop a deeper emotional bond that could lead to a romantic relationship. It could explore how their different personalities, Naruto's optimism and Tsunade's more hardened exterior, interact and complement each other.
In some 'naruto x tsunade time travel fanfiction', an interesting plot could be that Naruto and Tsunade travel back to a time when the Hidden Leaf Village was just being founded. They have to deal with the primitive and often dangerous situations of that era. Naruto might introduce some future - like ideas to help build the village, while Tsunade uses her medical skills and leadership to gain the trust of the early villagers. It's also possible that they face challenges from other ninja clans who are not so welcoming of their new - fangled ways.
Another plot could be that Tsunade uses her medical knowledge along with Naruto's power to go back in time and heal some of the major wounds the ninja world has suffered. They could go back to the time of the First Hokage and help him build a more peaceful and prosperous ninja world from the start. In this way, they might avoid all the wars and conflicts that followed.
They could be on a diplomatic mission together to another village. Along the way, they face various challenges like cultural differences and distrust from the other village. Through their combined efforts, they manage to overcome these obstacles and in the process, their relationship as comrades grows. This kind of plot can show their diplomatic and problem - solving skills while also exploring their relationship.
One interesting plot idea could be that Naruto and Kishina travel back to a time when the Uchiha clan was still intact. They could try to prevent the future tragedies that are related to the Uchiha. Another idea is that they go back to a time when the Hidden Leaf Village was first founded and get to experience the early days of the village's development. They might also have to deal with different power structures and rivalries that were present at that time.
One idea could be that Naruto and Kishina travel back to the time when the Uchiha clan was at its peak. They could try to prevent the future tragedies related to the Uchiha. Another could be them going back to the era of the First Hokage and learning about the origins of Konoha and how it was built. They might also discover secrets about their own clans that were lost over time.