One common theme is the betrayal of trust within the team. For example, a member might be secretly working for an enemy, like Loki infiltrating the Avengers and causing internal rifts. Another theme could be the betrayal of ideals. Maybe a hero becomes disillusioned with the Avengers' way of doing things and decides to take a different, more extreme path that goes against the group. Also, personal vendettas can lead to betrayal. If one Avenger has a long - standing grudge against another, it could result in actions that are seen as betrayal to the team as a whole.
Captain America could be a likely character to be betrayed. He represents the old - school values of the Avengers, and in a more modern, cynical world within fanfiction, some might see his ideals as outdated and turn against him. Also, Tony Stark. His wealth and sometimes over - confident attitude could make some of the other Avengers, especially those with more humble backgrounds, feel resentful and potentially betray him. And Thor, being an Asgardian, might be betrayed due to the other Avengers' mistrust of his alien nature or the potential threat Asgard could pose.
Peter could rely on his own inner strength. He has a strong moral compass, so he might use that to remind himself that the Avengers' actions are wrong, not his. And then he could focus on using his Spider - Man skills to prove his innocence or protect himself.
One possible storyline could be that Percy is forced to betray the Avengers due to some sort of mind control. Maybe an enemy has a powerful device or magic that compels him to act against the team. Another could be that Percy is misjudged by the Avengers. They think he has betrayed them because of some false evidence planted by a villain who wants to create chaos within the group. For example, a villain might make it look like Percy has leaked important information about the Avengers' plans.
Steve Rogers would probably be deeply disappointed. He values loyalty highly, and Tony's betrayal would shatter the trust they had. He would try to find out the reasons behind it and might even try to bring Tony back to the right path if he thought there was a chance.
Snape is a likely candidate. In the original series, his loyalties were always a bit of a mystery at first. In fanfiction, he could be further explored in terms of false betrayals or real ones. Another one could be Draco Malfoy. He was on the verge of becoming a full - blown Death Eater in the original, so in fanfiction, he could either truly betray his Hogwarts classmates or be wrongly accused of betrayal.
Another reason could be a difference in ideology. Percy might have had a different view on how to protect the world compared to the Avengers. He could have thought that their methods were too soft or too harsh, and decided that by betraying them, he could implement his own ideas better. He might have seen an opportunity to take matters into his own hands and make what he believed were the right decisions for the greater good, even if it meant going against the Avengers.
Well, in such fanfictions, one key event could be a character who was thought to be a loyal friend turning out to be a Death Eater spy. For example, a character like Seamus Finnigan might be made into a traitor in the fanfic, revealing secrets of the Order of the Phoenix to Voldemort. Another could be a teacher at Hogwarts, who, instead of protecting the students, betrays them to the dark side for power or fear. It really depends on the creativity of the fanfic writer, but often it involves the breaking of trust within the wizarding community.
Jealousy could be a major motive. Maybe someone is jealous of their talents, like their combat skills or their ability to make friends easily. For example, a less - skilled ninja might feel overshadowed and decide to betray them to get ahead.