It could be a vengeful god or goddess. Maybe one who has a grudge against the demigods in general and sees Annabeth as an easy target to send a message. For example, a minor god who feels overlooked and wants to prove their power by kidnapping such a well - known demigod.
The Titans or their followers might be the kidnappers. They might see Annabeth as a threat to their plans of overthrowing the gods. Since she's smart and strategic, they could want to keep her out of the way or use her knowledge against the gods and other demigods.
Another likely kidnapper could be a powerful and jealous demigod from another camp. They might be envious of Annabeth's skills and reputation. So, they kidnap her to steal her ideas or to make their own camp look better by making Annabeth's camp look weak without her.
The Joker is a likely kidnapper. He has a history of causing chaos and targeting the Bat - family. He might see kidnapping Batgirl as a way to get back at Batman or just for his own twisted amusement.
It could be a group of rogue ninjas. They might see Shikamaru as a valuable asset due to his intelligence and strategic skills. They could plan to sell him to the highest bidder or use him to carry out their own devious schemes.
It could be a rival athlete who is jealous of Serena's success. They might think that by kidnapping her, they can eliminate the competition. Another possibility is a deranged fan who has an unhealthy obsession with Serena and wants to keep her all to themselves.
A secret society that believes Mycroft is a threat to their hidden agendas. They may think that by kidnapping him, they can stop him from interfering with their plans. They would likely be very well - organized and have resources to keep him hidden.
It could be Kingpin. He has a long - standing feud with Daredevil (Matt Murdock). Kingpin might kidnap Matt to finally get rid of his nemesis once and for all or to use him as a bargaining chip against the other superheroes in Hell's Kitchen. Another likely kidnapper could be a new and emerging criminal gang that wants to make a name for themselves by taking out Daredevil. They might think that by kidnapping Matt, they can gain respect and control in the criminal underworld.
It could be a criminal mastermind who sees Shinichi as a threat to his illegal activities and Kaito as someone who can be used as leverage. Maybe a powerful underworld figure who has been on Shinichi's radar for a long time and decides to take action by kidnapping them both.
Maybe a secret admirer who is too shy to approach her normally. They think that by kidnapping her, they can have some alone time with her and confess their feelings. However, this is a very extreme and wrong way to go about it. Another possibility is a group of thieves who think Haruhi comes from a wealthy family and they can get a big ransom for her.
Another possibility is a deranged fan. If she has a large following, there could be someone who has an unhealthy obsession with her. This person might think that by kidnapping her, they can have her all to themselves and force her to be with them.
It could be a deranged follower of Voldemort. Voldemort was always after those who opposed him, and James and Lily were part of the Order of the Phoenix. So, a fanatic Death Eater might think that kidnapping them would be a great way to please their master.
There could also be a group of villains working together to kidnap Sonic. For instance, a combination of Eggman and some of his more powerful robot creations along with a couple of other villains from Sonic's rogues gallery. They might have a grand plan that requires Sonic's capture, like using his power to open a portal to a world full of chaos energy that they can then control.