One likely kidnapper could be Discord. He loves chaos and might see kidnapping Twilight as a great way to create chaos in Equestria. He could be bored and think that Twilight's absence would disrupt the harmony that she and her friends usually maintain. Another possible kidnapper is a jealous rival magician. Someone who is envious of Twilight's power and knowledge of magic and believes that by kidnapping her, they can steal her secrets and become the most powerful magic user in Equestria.
A likely kidnapper could be a power - hungry pony who wants to take over Equestria. They know that Twilight is one of the key protectors of the land and by kidnapping her, they can weaken the defenses. Also, there could be a magical creature that has a grudge against ponies in general and Twilight in particular. Maybe she accidentally disrupted its home or something while exploring magic. So it decides to kidnap her to teach ponies a lesson. There's also the possibility of a time - traveling villain who knows that Twilight will play an important role in the future and tries to stop it by abducting her in the present.
The Yiga Clan could be likely kidnappers. They've always been enemies of Link and would love to get their hands on him. They might see kidnapping him as a way to stop him from interfering in their plans. Another possibility is the Gerudo thieves. Although not all Gerudo are bad, there could be a group of them who think Link has something valuable and decide to take him hostage.
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.
It could be a jealous rival host club. They might be envious of the kidnapped host club's success and popularity, so they plan to kidnap them to gain an advantage.
It could also be a lone vampire with a vendetta against Kaname or the academy. This vampire might think that by kidnapping Yuki, they can exact revenge on Kaname or cause chaos within the academy. Yuki is an important figure in the Vampire Knight world, and her kidnapping would surely disrupt the delicate balance that exists.
Enemies from her past, such as old villains she's fought against, would be likely kidnappers. They might hold a grudge for her previous defeats and want to use her for revenge or some dark purpose.
Another possibility is a werewolf who has lost control or has a different agenda. In the Twilight universe, the werewolves and vampires have a tenuous relationship, and a werewolf kidnapping Bella could add a whole new layer of conflict. It could be a werewolf who doesn't trust Bella's relationship with the vampires and thinks she's a threat to their pack in some way.
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.
A jealous rival of Inuyasha might kidnap Kagome. For example, another demon who wants Inuyasha for himself might think that by taking Kagome, he can get Inuyasha to do his bidding. This would create a lot of drama and conflict between Inuyasha and the kidnapper.
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 Naraku would be a likely kidnapper. He is always plotting against Inuyasha and trying to get his hands on the Tessaiga. Kidnapping Inuyasha would be a way for him to either steal the sword or find a way to break Inuyasha's spirit so that he can no longer oppose him.