It could be Orochimaru. He's always been interested in Naruto's power and the Nine - Tails within him. Maybe he sees an opportunity to steal the Nine - Tails' power before the sealing process.
There's also a possibility that some rogue ninjas from within the Hidden Leaf village could be the kidnappers. They might be jealous of Naruto's status and power and want to disrupt the sealing to cause chaos in the village or gain power for themselves.
The Akatsuki is also a likely candidate. They were after the Nine - Tails for a long time. Kidnapping Naruto before the sealing would be a smart move for them to achieve their goals of collecting all the Tailed Beasts.
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 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.
The Sound Five might be the kidnappers. They are loyal to Orochimaru and would do his bidding. If he wants fem Naruto, they would be the ones to carry out the kidnapping. Also, Danzo could be a likely kidnapper. He has his own motives and ways of doing things in the village. He might see fem Naruto as a threat or an opportunity for his own gain and arrange for her to be kidnapped secretly.
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.