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.
In the long run, the Avengers' reaction might lead to a split in the team. Some members might be more forgiving and think they can bring Percy back to their side, while others would be too bitter about the betrayal to ever trust him again. This could cause internal conflicts within the Avengers as they debate how to deal with Percy and what their future actions should be.
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.
Iron Man would be angry. He'd probably use his technology to try and track Percy down. He might also start to review all the security protocols to make sure no other traitors could do the same. Thor would be more of the 'let's fight him head - on' type, but the other Avengers would have to hold him back until they have a proper strategy.
In a fanfiction, the Avengers' reactions to Percy Jackson's powers would be complex. Natasha Romanoff would immediately start thinking about how to use Percy's powers to their advantage in a mission. Bruce Banner, as the Hulk, might be a bit envious that Percy has such a natural and controlled power, while his own transformation is more of a chaotic force. Steve Rogers would be in awe of Percy's connection to an ancient power source, the Greek gods. And Clint Barton would probably make some jokes about Percy being like a human water hose, but deep down he'd be impressed. Tony Stark would want to incorporate Percy's power - controlling abilities into some new technology, or at least try to understand the science behind it.
Percy would probably be very confused at first. He's used to dealing with threats from the world of Greek mythology, not superheroes like the Avengers. But once he realizes he's been kidnapped, he'd likely be angry. He'd try to find a way to escape using his powers, like controlling water to create distractions or even using it to overpower his captors.
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.
Thor would be the most likely to relate to her on some level, as he comes from a world of gods and magic too. He might see her as an equal in a way. Bruce Banner would be interested in the scientific aspect of how her powers work, if there is any scientific explanation within the context of the fanfiction. And the others like Clint Barton and Wanda Maximoff would be curious about her background and how she ended up in their world.
Percy's reaction would be complex. On one hand, he would respect the Avengers' powers. He'd see Iron Man's intelligence - based powers as a different kind of 'gift' compared to his own demigod abilities. He might be a bit intimidated by the combined might of the Avengers at first. But then, he would start to analyze their powers. He would think about how Captain America's leadership and physical abilities are like the qualities of some of the heroes in his own world. And he'd be constantly comparing and contrasting their powers with his own and those of his friends, trying to find common ground or new ideas that could help him in his own adventures.
Percy would be angry. He has been through a lot in his own world and being betrayed again would not sit well. He'd probably lash out with his powers at first.
Bruce Banner, when he's not in Hulk mode, would be really interested in the scientific aspects that might be hidden in the Percy Jackson fanfiction. Even though it's a world of magic, he could look for ways that the magic could be related to some kind of scientific principle. He might also be interested in how the characters control their powers, whether it's Percy with his water powers or the Avengers with their various abilities, and look for similarities in self - control and management of power.
Percy would probably be very angry. He's used to being a hero, not a captive. He might immediately start trying to break free, using his water powers to create distractions or even attack if he feels really threatened.