It could be that Mr Evans is a time - traveler who goes back to the era of the Marauders. He might try to change some events that he knows are going to have bad consequences in the future. The fanfiction could show his struggles to fit in the past, understand the culture of that time, and his attempts to befriend the Marauders without revealing too much about the future.
Perhaps Mr Evans is a Muggle who accidentally discovers the Marauders' secret hideout. He then gets involved in their adventures, which could include things like sneaking out of the school grounds or dealing with dark creatures. It might also explore how the Marauders interact with an outsider like Mr Evans and how they either accept or reject him in their group.
Maybe Mr Evans is a wizard who has been living in seclusion for a long time. He comes out of his hiding when he hears about the Marauders and their adventures. He could be an old wizard with a lot of knowledge and skills that the Marauders could benefit from, or he could be someone who needs the Marauders' help to solve a personal problem.
Well, it could be about Teddy Lupin traveling back in time and meeting his father's friends, the Marauders. Maybe he gets to experience their pranks first - hand and learns some new magical tricks from them.
One common theme is friendship. Often, James and Mr Evans start off as strangers and gradually form a strong bond of friendship. For example, they might help each other through difficult times or share common interests.
One possible plot could be that Lily Luna Potter somehow travels back in time. She meets the Marauders in their Hogwarts days. Maybe she initially has trouble fitting in with their mischievous ways but then starts to understand their true natures. She could end up joining some of their adventures and perhaps even influence their actions in a way that has a positive impact on the future she comes from.
Perhaps Hermione meets the Marauders when they are in the middle of planning one of their big pranks. They might be suspicious of her at first, thinking she's a spy or something. But then, as they get to know her, they realize she's actually really brilliant. They could end up working together on a new kind of adventure that combines Hermione's intelligence and the Marauders' mischievousness, like solving a mystery in Hogwarts that has been long forgotten.
The fanfiction could show Albus Potter learning about the Marauders' values and how they formed their strong bond. He might be in a situation where he needs to form his own group of friends like the Marauders did. The Marauders could also help Albus deal with the pressure of being a Potter. For example, they could tell him how James Potter coped with all the attention he got, and this would give Albus some perspective on his own situation at Hogwarts.
One great 'James meets Mr Evans' fanfiction is 'The Unexpected Encounter'. It has a really interesting plot where James and Mr Evans meet in a very unusual setting, like an old, abandoned library. The author does a wonderful job of describing their initial shock and then the slow development of their relationship.
Another plot could involve the Marauders getting involved in a mystery that is plaguing Hogwarts in the present day. They use their old - school pranking skills and knowledge of the castle's secrets to solve it. They might have to team up with some of the current Gryffindor students who remind them of themselves when they were young.
In the fanfiction, Nico might find himself in some of the Marauders' pranks. Since the Marauders are known for their mischief, they could include Nico in one of their elaborate schemes against the Slytherins. Nico, being from a different background, might have a different perspective on these pranks and could either enhance them or try to stop them depending on his moral compass at that moment.
It's possible that they would have deep conversations. They could discuss the concept of sacrifice, as Fred sacrificed himself in the war. The Marauders, having lost their lives too, could relate to his experiences. They might also talk about the importance of friendship and how it transcends death. Fred could find a new sense of belonging with the Marauders in heaven, creating a bond that is both unique and heartwarming.