How could he escape?

Naruto could try to befriend some of the Kumo ninjas who might not be in favor of the kidnapping. By winning them over, they could help him escape. Also, he could use his knowledge of ninja techniques and his quick thinking. For example, he could use substitution jutsu to switch places with an object when the guards are not looking and then make a run for it.

Naruto could use his ingenuity and ninja skills to escape. Maybe he'd find a way to hack into the system using his chakra in a unique way. Since he's used to finding solutions in tough situations in his own world, he might discover a hidden loophole in the SAO system.

Naruto could use his shadow clones to create distractions. He could make a large number of clones and while the Akatsuki members are dealing with the clones, he could find an opening to escape. Also, he might be able to tap into the power of the Nine - Tails more than ever before in a desperate situation, using its strength to break free from any restraints.

Percy could look for any weaknesses in the wizards' magic or their security. Maybe there are certain times of day when their spells are less effective. He could also try to befriend a less - strict wizard who might be willing to help him escape.

Naruto could use his Rasengan to create a big enough explosion to scatter the mob and then make his escape. He might also use his speed to quickly dash through the crowd and find a hiding place.

Percy could use his water powers. He could summon water from nearby sources, like pipes or even the air if it's humid enough. With the water, he could create distractions, like water walls or waves to disorient the Avengers. Then he could make a run for it.

In fanfiction, Naruto has a lot of ways to escape from Akatsuki if kidnapped. He could wait for an opportunity when the Akatsuki members are preoccupied with their internal disputes. Since he has a strong bond with his friends in Konoha, they might be on their way to rescue him. Naruto could also use his unique Uzumaki bloodline abilities, like his strong life force, to endure any torture or imprisonment until he finds a way to get out. He might even discover some secrets about the Akatsuki during his captivity that could be used to his advantage.

Well, first of all, Percy is a very resourceful character. If he was captured by SHIELD, he'd quickly assess his surroundings. Since he has control over water, he could start by causing a water - related malfunction. For example, if there were any water - cooled systems in the SHIELD facility, he could make them burst. This would create chaos and give him an opportunity to slip away. He could also use his powers to sense any water sources around, like underground water channels. He could then use these as a means of escape, perhaps creating a tunnel of water to swim through. And don't forget his sword, Riptide. He could use it to cut through any barriers or fend off agents if necessary.

He could use his Rasengan. If he manages to gather enough chakra secretly, he can surprise his captors with a powerful Rasengan and break free.

Harry could use a powerful disillusionment charm. This would make him blend in with his surroundings so well that SHIELD agents would have a hard time finding him. He could then make his way to an exit while they're distracted. Also, if he had his wand on him, he could perform a series of diversionary spells, like creating a false image of himself to draw their attention away while he escapes.