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.
In this fanfiction, it could be that the future has a new Dark Lord. The Marauders are brought forward in time to stop this new threat. They face challenges like understanding the new forms of magic and technology that the future Dark Lord has harnessed. They also have to deal with the fact that the future wizarding world has different social and political structures. They might start by infiltrating the Dark Lord's lair using their Marauder's Map - like skills, but find that the map doesn't work as well in the future, leading to all sorts of interesting and dangerous situations.
He could meet his future self. This encounter might be full of surprises as his future self could have different views and experiences. His future self might be more jaded or more powerful.
One idea could be time travel in the fanfiction. The main character goes to the future and discovers a world where technology has both saved and endangered humanity. For example, there are flying cars but also a great divide between the rich who can afford advanced healthcare and the poor who can't.
In such a fanfiction, perhaps the Avengers could be shocked by how much Peter has grown and developed in the future. He might show off new powers or skills he's acquired. For example, his Spider - Sense could be even more advanced, allowing him to predict complex threats far in advance. And he could offer new perspectives on old foes the Avengers have faced, based on his future experiences.
He could meet his future self. This would be a very interesting encounter as he could learn from his future self about what he has accomplished and what mistakes he should avoid. He might also meet the future generations of his family, like his grandchildren or great - grandchildren.
Obviously, the Marauders themselves - James Potter, Sirius Black, Remus Lupin and Peter Pettigrew would be the main characters. They are the ones 'meeting' the future after all.
Perhaps he would meet historians or scholars of his own time. They could have traveled to the future too and are now studying how his actions in the past have led to the present - future situation. It would be an interesting encounter as they could discuss the different interpretations of his life over time.
Well, they might face some new and advanced vampires. Maybe the future vampires have developed different powers or abilities that the Cullens have never seen before.
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.