Maybe it's a criminal mastermind that Drake has been getting too close to in his investigations. This person sees Drake as a threat and decides to kidnap him to halt his progress. It could be someone who has a lot to lose if Drake exposes their illegal activities, like a powerful underworld figure running a large - scale smuggling operation.
It could be an old acquaintance from his past who has turned to the dark side. Maybe someone he once trusted during one of his earlier adventures but who has since become jealous of Drake's success and wants to use him to get rich quick. For example, a former partner who was left behind in a previous treasure hunt and now blames Drake for his misfortunes.
Perhaps Drake is kidnapped because he has uncovered a dark secret in Ripper Street. The kidnappers could be trying to silence him. His captors might hold him in an abandoned building, and he has to use his wits to try and escape while his colleagues search the seedy underbelly of the street for him. This could involve a lot of tense moments as the kidnappers threaten him and his friends get closer to finding him.
It could be an old enemy of Keith's, someone from his past who has a vendetta against him. Maybe a former rival from his days in the military academy who has now turned to more devious means.
In some creative fanfiction, it could be an alternate version of Spiderman himself from a different dimension. This Spiderman has gone bad and kidnaps a fan from our dimension as part of some grand, dark plan that involves crossing dimensions and causing chaos.
A power - hungry nobleman from a neighboring land could be the kidnapper. He might believe that by having Rapunzel in his possession, he can gain some sort of political advantage or use her as a bargaining chip against her kingdom.
It could be Orochimaru. He's always been interested in obtaining powerful individuals for his experiments, and Naruko with her unique abilities would be a prime target.
It could be a new villain that has emerged, someone who is jealous of Gohan's power and wants to make it his own. This villain might be from a far - off planet and has heard of the Saiyan legend.
It could be a group of rogue Decepticons who are acting on their own. They might not follow Megatron's orders but still see value in kidnapping Arcee. Maybe they have a personal vendetta against her or think they can get rich by selling her to the highest bidder in the Cybertronian underworld.
Maybe it's a group of villains working together. They could be from different factions but united by the idea that Izuku has the potential to become a huge threat to their plans. They might kidnap him to either eliminate him or turn him to their side. Also, it could be a lone, obsessed fan of a villain who wants to prove themselves by bringing Izuku to their idol.
A group of outcasts from different islands might kidnap Moana. They feel that they have been wronged by the 'normal' society that Moana represents. They hope that by kidnapping her, they can get the attention they deserve and force the islands to change their ways. But Moana listens to their grievances and tries to find a way to help them while also finding a way home.