Perhaps Loki kidnaps Harry Potter because he's bored in the Asgardian realm and sees the wizarding world as a new playground. He could be curious about the magic there and figures Harry is the key to understanding it all. He might take Harry to different magical locations, forcing Harry to show him the secrets of the wizarding world.
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.
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.
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 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.
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 possible plot could be that Loki, for some reason, was banished to the wizarding world long ago. He fell in love with a witch and had Harry. As Harry grows up, Loki reveals himself and starts training Harry in a more unorthodox form of magic. Along the way, they have to face the Ministry of Magic's suspicion as Loki's actions are often hard to understand. Also, they would have to deal with Voldemort, with Loki using his cunning to outwit the dark wizard.
Well, perhaps Harry could use his magic skills like the Patronus charm to hold Loki at bay. Since Harry has experience dealing with dark forces, he might be able to outwit Loki's trickery.
Well, perhaps Harry Potter, in the guise of Loki, uses his trickery skills in the wizarding legal system. He could be defending those wrongly accused of using dark magic, like using his shape - shifting abilities to find evidence that others can't.
One possible plot could be that Harry starts to show Loki - like traits early on at Hogwarts. He might use his trickery to outwit his enemies, like the Malfoys. Maybe he even uses some of Loki's shape - shifting abilities in a magical way to get out of tricky situations during his adventures.
One possible plot could be that Loki, reincarnated in the Harry Potter world, is initially confused by his new surroundings. He then discovers that his powers are still there but manifest in different ways in the wizarding world. He might get involved in the fight against Voldemort, not because he's on the side of good, but because he sees an opportunity for chaos and power. Along the way, he forms unlikely alliances with some of the Hogwarts students, who are both intrigued and wary of him. And his presence might also disrupt the normal order of the wizarding world, causing new problems and solutions to emerge.
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.