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.
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.
At first, Percy could be in shock. He can't believe that the gods, whom he has served and trusted, would betray him. But then, as the reality sinks in, he might become determined to get justice. He starts to plan his next moves carefully, using his wits and the skills he has learned over the years. He may also feel a sense of sadness and loneliness, as he realizes he is now on his own against the powerful gods.
One possible reason could be that his friends wrongly accused him of something major. For example, if they thought he was secretly working for an enemy and didn't give him a chance to explain. Another reason might be that the gods themselves turned against him unjustly, perhaps because they feared his growing power and influence. This could make Percy feel so alone and betrayed that he decides to join Chaos as a form of revenge or to find a new place where he is accepted for who he is.
One possible reason could be jealousy among his peers. Maybe someone was envious of Percy's skills or popularity and spread false rumors about him, leading to his betrayal. For example, if Percy had a special power or was favored by a certain group, others might feel left out and decide to turn against him.
In fanfiction, one possible motive could be his sense of duty. Percy has always been one to follow rules and uphold order. So, when faced with a great threat, he might sacrifice himself because he believes it's his duty to protect others, just as he has always tried to protect the integrity of the wizarding institutions he was part of.
One possible reason could be jealousy. Maybe Percy has some special abilities or achievements that make others envious. For example, his connection to the sea could be seen as a huge advantage that others might resent. Another reason could be misinformation. Someone might spread false rumors about Percy, leading others to believe he's done something wrong when he hasn't. It could also be that there's a misunderstanding about his relationship with Annabeth. Some might think he's getting special treatment from her or the other way around, which causes them to turn against him.
They were probably shocked at first. I mean, they trusted Percy, so it would be a huge blow. They might have felt angry and deceived.
Power could also be a factor. Suppose there's a powerful object or ability that only one of them can have. Travis may be tempted to betray Percy to get it for himself. He might think that with this power, he'll be more respected in the camp.
Percy might initially be confused. He might start to question everything that led up to the betrayal. His mind could be racing, trying to figure out if there were any signs he missed. He might also be hurt, but the confusion could overshadow the pain at first as he tries to make sense of the situation.
One possible motive could be some sort of mind control. Maybe a powerful enemy has the ability to control Percy's actions and forces him to go after Artemis. This would add an element of tragedy as Percy would be acting against his will.