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.
It could also be that Loki is being controlled by some other powerful force. This force wants Natasha for her unique abilities. Loki, being under the influence, kidnaps her. Natasha, being the tough spy she is, tries to resist and find a way to escape while also trying to figure out who is really behind her kidnapping.
Well, perhaps Loki kidnaps the Hulk to use his strength in some scheme against the Avengers. Maybe he wants to use the Hulk to break into a secure location or as a weapon against Thor.
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.
Another plot twist could be that the reader has some sort of power or knowledge that Loki needs. So, instead of a malicious kidnapping, it's more of a strategic move on Loki's part. He might be trying to bargain with the reader to get what he wants, but as time passes, he starts to develop feelings for the reader.
One possible plot twist could be that Loki actually has a noble reason for kidnapping Tony. Maybe he wants to use Tony's intelligence to stop a greater threat that the other Avengers are unaware of. For example, there could be a hidden enemy that Loki has knowledge about, and he believes only Tony can help create a device or strategy to defeat it.
One possibility is that Loki wants to use Harry's magical abilities for his own devious plans in the wizarding world. Maybe he thinks Harry's connection to Voldemort could be exploited to gain power over both the magical and non - magical realms.
In this fanfiction, it could be that Loki was misled into thinking the girl was an enemy spy. So, he kidnaps her to interrogate her. However, during the interrogation, he discovers she's completely innocent. Now, he has to figure out how to make up for his mistake without losing his pride, and also deal with the potential chaos that his hasty action has caused among her friends and family.
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.
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.
Perhaps Loki kidnaps Captain America to prove a point. He may believe that the so - called 'good guys' are not as invincible as they seem. He could subject Captain America to various mental challenges, trying to break his will and show the world that even the most noble heroes can be corrupted. But Captain America's strong moral compass will likely make it very difficult for Loki to succeed.
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.