A cool plot idea could be Minato traveling back to his own childhood. He could then use his future knowledge to train himself more effectively, making himself an even more powerful shinobi at a younger age. This would have a huge impact on the future of the Leaf Village as he would be able to better protect it earlier. He might also be able to prevent some of the early tragedies that happened in the village.
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.
One idea could be that Minato and Kushina travel back to the time when the Hidden Leaf Village was first founded. They could use their modern - day knowledge and skills to help shape the village in new ways, like introducing new jutsu training methods. Another could be that they go back to a time when a great war was about to start and they use their powers to prevent it, thus changing the future of the ninja world.
Another plot could involve Minato traveling back in time and meeting his parents. He could learn more about his family's past and secrets that were lost over time. This could lead to him unlocking new powers or abilities that were somehow related to his family heritage. He might also be able to use this new - found knowledge to better protect the village in his original time.
Well, perhaps a plot twist is that when they time travel, they end up switching bodies. Naruto, in Minato's body, has to deal with the responsibilities of being a Hokage in the past, while Minato, in Naruto's body, has to navigate through Naruto's life in the present. This would create a lot of comical and also very tense situations as they both try to adapt and not mess up the timeline.
One interesting plot twist is if they time travel and find that the world they end up in has a different version of the Chakra system. They have to adapt quickly to this new form of energy while also trying to find a way back home. Also, imagine if they time travel and discover that Naruto was supposed to be born in a different village in this alternate timeline. This would completely change the way they view Naruto's destiny and their role in protecting him.
One interesting plot could be Minato traveling back to prevent the Nine - Tails attack on Konoha. He could use his knowledge of future events to stop Orochimaru from influencing the situation that led to the attack. Another plot might be Minato traveling to a time when the Uchiha clan was on the verge of the coup. With his wisdom and power, he could try to find a peaceful solution and prevent the massacre. Also, he could travel to the time of the First Hokage to learn more about the origin of the ninja world and bring back that knowledge to improve Konoha in his own time.
One interesting plot could be Minato and Naruto going back in time and Minato getting to see Naruto grow up from the start. He could teach Naruto things he didn't get to in the original timeline, like more advanced jutsu. Another plot might involve them changing key events in the past that had a major impact on the future of the ninja world. For example, preventing certain tragedies or battles.
One idea could be a story where baby Naruto somehow gets a vision of his father Minato's past battles. This would be really cool as Naruto could start showing early signs of his future strength inspired by his dad. Another plot could be Minato coming back briefly as a spirit to protect baby Naruto from some early threats that Kakashi or the Third Hokage might not be aware of.
One idea could be a body - swap situation where Naruto wakes up in Minato's body during Minato's time. He could use his knowledge of the future to change some events and prevent certain tragedies. Another could be Minato taking over Naruto's body for a short time to experience how far the village has come and to give Naruto some hidden power or knowledge that only he could provide as his father.
One idea could be that Naruto travels back in time and gets adopted by a different clan. For example, the Uchiha clan. This would change his whole upbringing and how he views the world. He might learn different jutsus earlier and have a different relationship with Sasuke.