She might try to manipulate Loki. Natasha is very good at getting into people's heads. She could play on Loki's ego or his own insecurities to gain an advantage. For example, she could pretend to be interested in his plans or offer to help him in some way, all while secretly planning her escape.
One possible plot could be that Loki kidnaps Natasha to use her as a bargaining chip against the Avengers. He might think that her skills and the Avengers' attachment to her would make them more likely to give in to his demands.
At first, Bruce might be scared. He knows Loki's reputation for being unpredictable and dangerous. But he also tries to keep his cool because he doesn't want to accidentally transform into the Hulk right away. He might try to reason with Loki, using his intelligence to talk his way out of the situation.
In some cases, the reader could be in a state of shock and disbelief. They might not believe that this is really happening. But as they come to terms with the situation, they could start to form a plan. Maybe they try to appeal to Loki's better nature, if they believe he has one, by talking about his past actions and relationships that show his capacity for good.
Thor would be furious. He would immediately start looking for Jane, using all his resources. He might first try to reason with Loki, but if that doesn't work, he would not hesitate to use force.
Captain America would probably remain calm at first. He's used to being in tough situations. He'd try to talk to Loki, reason with him, and find out what Loki wants.
One possible scenario in this fanfiction could be that Loki disguises himself and lures Spiderman into a trap. He then transports him to a different realm where Spiderman is completely out of his element. Spiderman would have to rely on his wits and basic powers to try and escape Loki's clutches.
If Loki kidnaps Spiderman in fanfiction, it would be a very interesting plot. Loki is a powerful and cunning character, while Spiderman is a beloved hero. Loki might underestimate Spiderman's resourcefulness though. Spiderman could use his spider - sense to find weaknesses in Loki's plans.
One possible outcome in this fanfiction could be that Loki kidnaps Darcy for a very specific reason. Maybe he needs her knowledge of some scientific concept that is relevant in the world he is from or is planning to use in his schemes. For example, if Darcy has been working on some sort of energy research that Loki believes can be harnessed for his own power - enhancing purposes.
One common theme is the clash of personalities. Loki is often depicted as a complex and somewhat devious character, while Natasha is very shrewd and calculating. Their interactions usually involve a lot of mental sparring. Another theme is redemption. Sometimes Loki is on a path to redeem himself and Natasha plays a part in that journey. For example, she might be the one to believe in his potential for good when others don't.
It could be someone who is manipulating Loki to kidnap the Hulk. Maybe an even more powerful villain from the Marvel universe, like Thanos. He might be using Loki as a pawn to get the Hulk for his own evil purposes.