One plot twist could be that the kidnappers turn out to be working for someone Juvia thought was a friend. Another could be that Juvia has a hidden power that she discovers while being held captive, which helps her escape. Or perhaps the person who seems to be the main kidnapper is actually being blackmailed into doing it.
Well, in a 'Juvia gets kidnapped' fanfiction, a great plot twist could be related to the rescue. Maybe the ones who come to save her are not the expected characters. For example, a character who has been in the background all this time, like a minor guild member, steps up and has some special knowledge or skill that is crucial for the rescue. Also, it could be that Juvia is kidnapped to be used as a bait for a much larger scheme, and the real target is actually her whole guild. When she realizes this, she tries to find a way to warn them, even from captivity.
One possible plot twist could be that the kidnapper is actually an ally in disguise, trying to protect Mario from a greater threat. For example, they might be taking him away from Bowser's clutches in a way that seems like a kidnapping but is really a rescue mission.
Well, a great plot twist might be that Ponyboy discovers the kidnappers are actually part of a secret society that has been observing him for a special reason. Maybe they think he has some hidden power or knowledge. Also, it could be that during the kidnapping, Ponyboy finds out that there is a traitor among his own group who helped the kidnappers. This would add a whole new layer of drama and mystery to the fanfiction.
One possible plot twist could be that the kidnapper is someone from Reid's past that he thought was long gone. Maybe an old unsub who escaped prison and is seeking revenge. Another could be that Reid is kidnapped as a means to get to the BAU team, and the kidnapper is using him as bait to draw out the whole team for a bigger attack.
It could be a rival guild member who wants to use Juvia as leverage against Fairy Tail. Maybe someone jealous of her powers or her relationship with Gray.
One common plot twist could be that the kidnapper is someone Allen thought was a friend all along. It adds a sense of betrayal and shock to the story.
In some fanfictions, a plot twist could be that Haruhi's kidnapping is part of a virtual reality game that she unknowingly entered. The 'kidnappers' are just players in the game who are trying to win by capturing her. Another common plot twist is that the kidnapper has a change of heart halfway through. They start to see Haruhi's good qualities and instead of harming her, they end up helping her. And sometimes, it could be that the kidnapping is a test set by a mysterious organization to see if Haruhi is worthy of some special task or knowledge.
Well, the fanfiction could be that Esme gets kidnapped while she is on her way to an important event. The kidnappers might be holding her for ransom. Her friends then start to look for any clues. They might find out that the kidnappers have a secret hideout in an abandoned building. So they plan a rescue mission, but they have to be careful as the kidnappers are well - armed and dangerous.
It could be that Ginny is kidnapped because she has some special knowledge or power that the kidnappers want to exploit. Her friends form a team to rescue her. Along the way, they discover more about the kidnappers' motives and the true nature of Ginny's importance. There would be elements of mystery, adventure and friendship in the fanfiction.
Well, perhaps Voldemort's followers could kidnap Harry to use him as a bargaining chip. They might hold him in an old, dark wizarding house, guarded by dark magic. Harry would then try to escape using his own magic skills and the help of some unexpected allies like house - elves who secretly oppose Voldemort.
Maybe it's a new villain in the fanfiction. This villain could be after Luigi because he thinks Luigi has some sort of special power or knowledge. So the villain kidnaps Luigi in a very sneaky way, like using a magic spell to put Luigi to sleep first and then whisking him away to a secret lair hidden deep in a dark forest.