One possible plot twist could be that Aizen has a hidden motive other than just causing chaos. Maybe he kidnaps Ichigo to use his unique powers for some sort of experiment. For example, he might want to extract the power of Ichigo's Hollow side to enhance his own strength or create a new type of Arrancar. Another twist could be that Aizen is being controlled by an even greater force, and Ichigo's kidnapping is part of a larger plan to draw out other powerful characters in the Soul Society.
Perhaps in the fanfiction, Aizen kidnaps Ichigo to make a statement. He could be trying to show the Soul Society that he can take their most powerful asset whenever he wants. This could lead to a situation where Ichigo's friends have to work together in a new and different way to rescue him. They might have to form unexpected alliances, like with some of the Arrancar who are also tired of Aizen's tyranny.
At the start, Ichigo would be defiant. He would not show any fear in front of Aizen. He might taunt Aizen, trying to get him to reveal his true intentions. As time goes on, he would start to feel a sense of isolation, but this would only strengthen his resolve. He would use his inner Hollow powers more freely, as he has no other option. He would also be constantly thinking about ways to turn the tables on Aizen and escape, and would be ready to take on any challenges that come his way during his captivity.
One idea could be that Aizen kidnaps them to use Ichigo's power and Rukia's knowledge of Soul Society for his own dark plans. He might want to study Ichigo's unique Hollow - Shinigami powers up close and use Rukia as a bargaining chip with Soul Society.
Well, one possibility could be that Grimmjow has some personal vendetta against Ichigo. Maybe he wants to use Ichigo as a bargaining chip with the Soul Society. He could be tired of Ichigo always getting in his way during battles and decides to take him to a secluded location where he can deal with him on his own terms.
One possible plot could be that Ichigo kidnaps Rukia out of a desperate need to protect her from some unseen and extremely dangerous threat in the Soul Society. He might believe that the Soul Society's own mechanisms for safeguarding her are insufficient.
A plot twist could be that the place they are captured in is not what it seems. It could be a magical or illusionary prison created by an unknown force. This would make their escape much more difficult as they have to figure out the true nature of the prison. Also, it could turn out that their capture was a self - fulfilling prophecy. Maybe Aizen's actions in the past led to a chain of events that resulted in their capture, but in a way he didn't expect. And Irukia could be the key to their escape, but he doesn't realize it until later in the fanfic.
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.
Well, perhaps the plot of the fanfiction where Sasuke kidnaps the reader could involve a misunderstanding. Sasuke might think the reader is working for his enemies when in fact they are not. As for the story development, it could lead to the reader gradually understanding Sasuke's past traumas and reasons for his actions, and in the end, they might even help him heal some of his emotional wounds. And there could be a lot of action scenes where the reader tries to escape but then realizes that Sasuke is not really a bad guy in this situation.
Well, one plot twist could be that Yassen is actually working for Alex's father all along and the kidnapping is a test for Alex to become a better spy. Another could be that Yassen kidnaps Alex but then realizes Alex has information that could save Yassen's own family, so they form an unexpected alliance. Or perhaps Yassen kidnaps Alex thinking he's someone else, and when he discovers the truth, he has to figure out what to do with this innocent boy in his custody.
Another idea is that the fanfiction could be a dark, alternate universe story where Jasper has turned evil. His reasons for kidnapping Bella could be tied to some sort of revenge plot against the Cullens. He might hold a grudge against them for something that happened in the past, and Bella is just a means to get back at them. This would create a very different dynamic compared to the original Twilight story.
In a Toga kidnaps Midoriya fanfiction, the plot could go in various directions. Maybe Toga kidnaps Midoriya to trade him for something she wants from the heroes, like the release of a fellow villain. Midoriya, on the other hand, could try to escape by using his wits and his knowledge of Toga's weaknesses. For example, if he figures out that she has a soft spot for a certain type of person or situation, he could use that to his advantage. Also, the story could involve the other students at U.A. trying to rescue Midoriya. They might come up with a clever plan that involves using their individual quirks in a unique way to outsmart Toga and get Midoriya back.