One possible plotline could be that Magnus Bane kidnaps someone in order to protect them from a greater danger. Maybe there's a powerful dark magic user after a young warlock, and Magnus takes the warlock to a hidden location. Another could be that Magnus is misjudged, and he actually didn't kidnap but was trying to rescue someone who was in a magically - induced coma and had to move them quickly. A third plotline might be that Magnus kidnaps someone as part of a deal with a demon, but then has a change of heart and tries to find a way out of the deal while keeping the kidnapped person safe.
In fanfiction where Magnus Bane kidnaps, it might be due to a prophecy. He might kidnap a person who is prophesied to either save or destroy the magical world. He takes this person away to train them or keep them away from those who would use them for evil. Another idea is that Magnus kidnaps a human who accidentally wandered into the magical world and he wants to keep them safe from the dangerous creatures there. He has to then deal with the human's fear and mistrust while also protecting them from other threats in the magical world.
The victim could be Alec Lightwood. Since Magnus and Alec have a complex relationship, a fanfiction could explore what would happen if Magnus kidnapped Alec, perhaps out of some miscommunication or a threat to Alec's safety that Magnus thought he could only handle by taking Alec away. Another potential victim could be a young, inexperienced warlock. Magnus might kidnap the warlock to teach them about their powers in a more secluded environment away from the prying eyes of the Shadowhunters.
One possible plotline could be that Keith is kidnapped by an enemy force. His friends then embark on a dangerous rescue mission, facing various challenges along the way. Maybe they have to infiltrate a heavily guarded enemy base to find and free him.
One possible plotline could be that Naruko is kidnapped by a powerful enemy who wants to use her as a bargaining chip against her friends or family. Another could be that she is kidnapped by a mysterious organization for some sort of experiment. Maybe she's kidnapped by someone who has a personal vendetta against her and plans to make her suffer.
Perhaps in this 'imprijt kidnapped fanfiction', the kidnapped person is a key figure in a grander scheme. Imprijt kidnaps them to use as a bargaining chip against their friends or allies. The friends then embark on a rescue mission filled with various challenges and unexpected twists.
One possible plotline could be that Stiles' friends immediately start a search. They might follow clues like strange footprints or a mysterious note left behind. Another could be that Stiles manages to outwit his kidnappers in some way while being held captive, perhaps by tricking them into revealing their weaknesses. Maybe the kidnappers are after something Stiles knows, like a secret about the supernatural world in the fanfiction's setting.
One possible plotline could be that Yami is kidnapped by a rival group who wants to use his special powers for their own evil deeds. His friends then embark on a dangerous mission to rescue him. Another could be that Yami is kidnapped as part of a ransom plot against someone he is close to, and they have to figure out how to meet the kidnappers' demands without sacrificing too much.
Well, it could start with Mycroft being lured into a trap and kidnapped. The kidnappers might be from a different dimension or have some sort of supernatural power. As the fanfiction progresses, Mycroft could use his wits to outsmart the kidnappers even while in captivity. There could be a lot of mind games and tense moments as he tries to escape or signal for help.
One possible plotline could be that a deranged fan kidnaps the Beatles in an attempt to force them to play a private concert just for them. Another could be that a rival music group arranges the kidnapping to try and stop the Beatles' rise to stardom.
One possible plotline could be that Aizawa is kidnapped by a group of villains who want to use his quirk knowledge against the heroes. They might hold him in a secret lair and try to force him to reveal the weaknesses of other heroes. Another plot could be that a deranged fan kidnaps him, believing that they can have a special relationship with him. The fan might keep him in a locked room, trying to convince him to like them back.
One possible plotline could be that Twilight Sparkle is kidnapped by a powerful dark magic user who wants to steal her knowledge of magic. Her friends then embark on a quest to rescue her, facing various challenges along the way. Another could be that she is kidnapped by an unknown force from another dimension for some sort of experiment. Her friends have to figure out how to cross dimensions to save her. A third plotline might be that a group of villains kidnap Twilight Sparkle to use her as a bargaining chip against Equestria, and her friends must find a way to outwit the villains and get her back safely.