In many fanfictions where Gil gets kidnapped, it could be for various reasons. Maybe it's by a rival group who wants to use him as a bargaining chip against his friends. For example, in some stories, Uma's crew might be targeted because they are seen as a threat in the Isle of the Lost. Gil, being a part of that crew, gets kidnapped. Writers often use this plot device to create drama and show the loyalty and courage of the other characters as they try to rescue him.
A more emotional plot idea could be that Nami gets pregnant by someone she loves deeply, but that person is lost or in danger. She then has to go through the pregnancy alone, with the support of the Straw Hat crew. The story could focus on her growth as she becomes a mother - to - be and how she overcomes the challenges without her partner.
Peter's kidnapping was a carefully planned event. The kidnappers had been observing him for weeks. One day, as he entered a park, they grabbed him. They blindfolded him and took him to a secluded location. Peter was scared but he didn't show it. He started to befriend one of the kidnappers, a young guy who seemed a bit hesitant about the whole thing. Peter told him stories about his life and gradually the kidnapper started to have second thoughts. Eventually, the kidnapper helped Peter escape by distracting the others.
It could be a new character created specifically for the fanfiction. Maybe a young scientist who is working on a project related to the super - soldier serum. Since Bucky has a history with the serum, this would create an interesting dynamic.
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.
One possibility is Dr. Eggman. He has always been after Sonic and wants to stop him. Kidnapping Sonic would be a way for him to achieve his evil goals.
Well, one possible plot could be that the kidnappers are after some valuable information that Castle has. Maybe it's related to a case he was working on and they think he knows more than he actually does. So they take him to a secret location and try to force him to talk.
Another possibility is that it's a group of mercenaries hired by a powerful underworld figure. The figure might want Nightwing out of the way so they can carry out their illegal activities more easily. The mercenaries would be well - trained and equipped, making it a difficult situation for Nightwing to escape from.
The kidnappers could be a group of hired mercenaries. Some powerful and wealthy person who has something to hide might have hired them. This person could be involved in illegal activities and Castle was on the verge of uncovering the truth, so they order the mercenaries to take Castle out of the picture.
It could be a rival gang. They might see Ponyboy as a threat or a way to get back at his own gang. Another possibility is a deranged fan of his, someone who has an unhealthy obsession and wants to keep him all to themselves. Or it could be a group of criminals who mistake Ponyboy for someone else who has something they want.