A mad scientist could be the antagonist. This scientist might believe that Tom Holland has some unique genetic makeup (because of his on - screen superhero persona) that could be used for their experiments. So, they kidnap him to conduct various tests. Or perhaps an evil wizard from a fictional realm (in a more fantasy - based fanfiction) kidnaps Tom because he believes Tom has the power to break a curse on his kingdom. Since Tom plays superheroes, the wizard might think he has real - life powers.
It could be a rival movie studio. They see Tom Holland as a threat to their own leading actors. So, they arrange for his kidnapping to disrupt his career and the production of his movies. Also, it could be a criminal gang that randomly targets celebrities for ransom. Tom Holland just happens to be their next victim. They don't care about his fame, just the money they can get from his kidnapping.
You can also start with a bit of mystery. 'There were rumors in the fandom, whispers that something was about to happen to Tom Holland. And then, on a seemingly ordinary day, he vanished. No one knew where he was, but there were signs that it was no ordinary disappearance.' This makes the reader want to keep reading to find out what happened.
One plot idea could be that the 'kidnapping' is a misunderstanding. Maybe a group of over - enthusiastic fans accidentally create a situation that looks like a kidnapping. For example, they surround Tom Holland in a chaotic scene at a fan event, and in the commotion, he gets separated from his security and ends up in a locked room with some fans, which is misconstrued as a kidnapping.
One possible plot could be that the kidnappers are actually fans who have gone too far in their obsession. They take Tom Holland, thinking they can have him all to themselves. Another could be that he's kidnapped as part of a ransom plot by a criminal group who wants a large sum of money from his management. Maybe it's also a case where a supervillain from one of his movie universes kidnaps him for some strange, other - worldly reason.
A powerful and corrupt business mogul could be the antagonist. He wants to use their fame for his own gain and when they refuse, he tries to destroy their careers. He spreads false rumors about them and tries to sabotage their projects.
It could be a new vampire who is jealous of Edward's relationship with Bella. This vampire might be from a far - off place and has heard about the Cullens and Bella. They decide to kidnap Bella to make Edward suffer. Another possible antagonist could be a human who has a grudge against the Cullens. Since Bella is associated with them, they target her. For example, a human whose family was attacked by a vampire in the past and blames the Cullens for not preventing it. They think that by kidnapping Bella, they can get back at the Cullens.
Perhaps an escaped convict who has a grudge against the Reagan family in general and sees Jamie as an easy target. This convict might be looking to use Jamie as a bargaining chip to get out of the country or something similar.
A rogue shinobi who has a personal vendetta against Sakura or her friends. Maybe this shinobi blames Sakura for something that happened in the past and decides to kidnap her as revenge. He could be a powerful and unpredictable antagonist.
It could be Doji. He's always been after powerful beyblades and Gingka's Pegasus is one of the strongest. He might kidnap Gingka to get Pegasus and use its power for his own dark plans. Another option is Ryuga. Although he has his own code, in some fanfictions he could be desperate enough to kidnap Gingka to prove his dominance in the beyblade world. Also, a new and unknown blader who is jealous of Gingka's skills and popularity could be the antagonist and kidnap him to make a name for himself.
The main antagonist could be Shere Khan. He has always been a threat to Mowgli and might see kidnapping him as a way to finally get rid of the 'man - cub'. He could be working with some of his sly jackal minions to carry out the kidnapping.
Star would be a likely candidate to rescue Marco. She has strong magical abilities and a deep friendship with Marco. She would stop at nothing to find him and bring him back safely.