He could meet his future descendants. Maybe a great - grandson who has inherited some of his speed but also has unique abilities of the future.
There's a chance that Minato meets future villains. These villains could be after his knowledge of the past or his unique abilities. Meeting them would put him in a difficult situation where he has to use his wits and powers to either defeat them or find a way to co - exist with them while he tries to figure out how to return to his own time.
A possible plot could involve Minato traveling to a future where the concept of chakra has evolved. He has to adapt to this new form of chakra usage. Along the way, he meets his own descendants and realizes the long - lasting impact of his actions in the past. He also tries to find a way back to his own time while making a mark in this future world.
It could be a rogue ninja from the future who follows them back in time. This ninja might have some vendetta against Minato or Kushina or wants to change the past for his own evil purposes. Maybe he wants to prevent Minato from becoming the Fourth Hokage so that he can take over the village in the future.
Naruto might encounter future versions of the kages from different villages. These kages could have different leadership styles influenced by the development of the future world. He may also run into new characters who have emerged as heroes or villains in this new era.
In this fanfiction, Sakura might be on a mission to change the past in order to save someone important in her present. Minato could initially be suspicious of her but then come to trust her as they face common enemies. They could end up influencing each other's future and past in unexpected ways, like Sakura teaching Minato some basic first - aid knowledge that he then passes on, which changes the course of some future battles.
A young scientist would be a great main character. They could be curious about what the future holds for their research and accidentally stumble upon a way to travel to the future. Their scientific knowledge would help them understand the new technologies and concepts in the future world.
When the Marauders travel to the future in a fanfiction, they may meet the students of Hogwarts in that future time. These students could be very different from the ones they knew in their own time. The Marauders might also come across future wizards and witches who are experts in new areas of magic that the Marauders have never even heard of. Additionally, they could meet people who are working on projects to preserve the history of the wizarding world, and these people might be very excited to meet the Marauders who are a significant part of that history.
He could meet Native American tribes. Elrond would be intrigued by their unique cultures and spiritual beliefs. He might exchange knowledge with them, like sharing elven tales in return for learning about their hunting techniques.
Cell could still be a great antagonist. Imagine a scenario where in the fanfiction, Cell follows Future Trunks through time. He then starts to absorb different beings in the new timeline in a more devious way than in the original story.
It could be a future version of Orochimaru who has found a way to come back even more powerful. Maybe he has developed some new form of immortality and is causing chaos in the future world that Naruto travels to.
It could be an unknown shinobi from a far - off land who has some sort of vendetta against Konoha. They might see this shinobi causing chaos in the future and start preparing to face him in the present.