Well, in a Naruto x Tobirama time travel fanfiction, it could be that Naruto is sent back in time to right before Tobirama's death. Naruto, being Naruto, tries to save Tobirama. Tobirama is initially suspicious of Naruto but then realizes his good intentions. Together, they work on a plan to make the ninja world a better place even before Hashirama's time. They could come up with new ways of training ninjas, ways that are more inclusive and less likely to lead to clan rivalries. This would then change the course of the entire Naruto universe.
One idea could be Tobirama traveling to the future and seeing how his village has developed. He might be shocked by the new technology and the different ninja techniques. Another plot could involve Tobirama going back in time to change a crucial event in Naruto's past, like preventing the Uchiha massacre. Or perhaps he travels to a different timeline altogether and has to find a way back while dealing with that timeline's unique challenges.
One interesting plot idea could be exploring their early days before the founding of the village. Maybe a story about a dangerous mission they went on together that strengthened their bond. For example, they could be facing a powerful enemy that forces them to rely on each other's unique skills. Tobirama's strategic mind and Hashirama's raw power could combine in unexpected ways to defeat the foe.
One idea could be Naruto time - travels back to Tobirama's era. He could use his modern - day knowledge and jutsu to help Tobirama in some great battles. Maybe Naruto teaches Tobirama about the concept of true friendship among different clans, which could change Tobirama's views on some policies he had for the clans.
One interesting plot idea could be a time - travel scenario where Sakura is somehow sent back in time to the era of Tobirama. She could use her modern medical knowledge to help in his village, and in the process, they start to develop feelings for each other. Another idea is that Tobirama is resurrected in the modern era where Sakura lives. He has to adapt to the new world, and Sakura helps him. During this, a relationship blossoms.
A really interesting plot could be that Tobirama is reborn as a non - ninja, but still has his chakra control abilities. He has to find a way to use his skills secretly while living a normal life at first. As he discovers more about the world he's in, he starts to influence the ninja world from the outside, creating a whole new dynamic in the story.
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.
One interesting plot idea could be that Naruto travels back in time and meets a young Mikoto. He could end up influencing the events that led to the Uchiha massacre in some way. Maybe he tries to prevent it by changing the relationship between the Uchiha clan and the village.
Maybe they travel back to a time when a great threat was about to destroy the village but was forgotten in history. Naruto and Kyshina, with their combined strength and knowledge of future jutsu, are able to defeat the threat and rewrite history so that the village doesn't suffer the losses it originally did. This could also lead to new relationships being formed between different characters who might not have interacted in the original timeline.
One idea could be that Naruto and Tenten travel back to the founding of Konoha. They could use their modern knowledge to influence the village's early development, like introducing new training techniques. Another could be that they go back to a time when a great battle was about to start and they change the outcome, thus changing the future of the ninja world.