In this fanfiction, it could be that Peter snaps after Tony makes a decision that Peter strongly disagrees with. Let's say Tony decides to sacrifice a certain group of people to save the majority in a moral dilemma. Peter, who has a stronger sense of justice for the individual, snaps and decides to go against Tony's plan. He then has to fight not only the external threat but also deal with the rift he has created within the team.
Well, clearly Peter Parker and Tony Stark are the main characters. Peter is the one who 'snaps' in this scenario, which means he has a significant character shift from his normal self. Tony, on the other hand, serves as a sort of contrast or the catalyst for Peter's snapping. Even though Peter is the one with the new behavior, Tony's presence and actions are likely to be integral to the story as they are what cause Peter to snap.
One possible plot development could be that Peter is left with a huge sense of guilt. He might struggle with survivor's guilt, constantly thinking that it should have been him. He could then become overly reckless in his superhero activities, trying to prove that he was worthy of being saved. Another aspect could be how the other Avengers deal with Tony's death. They may turn to Peter as a symbol of hope, since Tony sacrificed himself for Peter. This added pressure on Peter could lead to him either rising to the occasion or crumbling under it.
Maybe Peter inherits Tony's high - tech gadgets. For example, he could get access to some of Tony's Iron Man tech, which would be a huge deal. This could set him on a new path in his superhero journey, perhaps allowing him to upgrade his own suit or develop new abilities.
One possible plot could be that Peter has continuously disobeyed Tony's safety instructions while working in the lab or on some high - tech projects. Tony, out of frustration and a sense of responsibility, resorts to this rather extreme form of discipline. However, this kind of plot would be quite controversial and not in line with the general positive and heroic image of their relationship in the mainstream stories. It would also be a very different take on their characters, showing a more authoritarian side of Tony.
Perhaps Steve leaves because of a personal sacrifice. He might discover that his presence is putting Tony and Peter in danger, like there's a villain targeting those close to him. So, to keep them safe, he leaves without much explanation. It could also be that he has some unfinished business from his past that he has to attend to alone, which forces him to part ways with Tony and Peter.
The 'tony is dusted instead of peter fanfiction' could have a very interesting plot. Since Tony is such a central and resource - rich character, his sudden dusting would be a huge shock. Pepper would be devastated. Peter, on the other hand, would be in a difficult position. He might try to use his own powers and intelligence to figure out a way to bring Tony back. The other Avengers would be looking to him for leadership in some ways, as he was the one closest to Tony among the younger heroes. And the whole dynamic of the post - 'dusted' world would be completely different from what we saw in the movies, with new alliances and strategies being formed in the absence of Tony.
Well, one possible change could be that the Avengers' dynamic is severely disrupted. Tony was a key figure in terms of resources and leadership. Without him, the remaining Avengers might struggle more in their fight against Thanos. Peter, on the other hand, being young and full of potential, his presence could have added a different kind of energy to the post - snap world. Maybe there would be more of an emphasis on the younger generation of heroes stepping up earlier.
One possible scenario in such a fanfiction could be that Peter, in a self - sacrificing move, takes on a powerful enemy that was originally meant to target Tony. Maybe Peter's inexperience and pure heart lead him to misjudge the danger, and he ends up giving his life to save others, while Tony is left to grapple with the guilt.
In the fanfiction world, there could be a prophecy or a pre - determined fate that Tony believes in. He may think that Peter's sacrifice is necessary to fulfill this prophecy and save the world from some greater threat related to the Soyl Stone. He might see it as a selfless act in the long run, even though it seems cruel.
A possible plot development could be that Peter is initially shocked by Tony's confession. He might not know how to respond at first, leading to some awkward moments between them. Then, they could gradually grow closer and form an even stronger alliance.