It could also be for protection. Bucky might have seen that the OC was in danger from other more malicious forces. His way of protecting the OC, albeit a very extreme one, was to kidnap them and keep them in a 'safe' location away from those threats.
One possible motive could be misinformation. Maybe Bucky was misled to believe the OC was a threat to someone he cares about. So, he kidnapped the OC to prevent them from causing harm.
Perhaps it's about love in a twisted way. Sebastian might be obsessed with Clary and think that by kidnapping her, he can make her his. In some fanfictions, characters with a warped sense of love do extreme things like this. He could also be trying to use Clary as a pawn in a larger scheme against the Shadowhunters. By having her in his control, he can manipulate the situation to his advantage.
Maybe Dumbledore believes that Harry has some hidden power that is being corrupted by the environment at Hogwarts. So, he kidnaps Harry to a secluded place to train him and help him control this power without any distractions or negative influences from other students or even some of the teachers.
One possible motive could be his thirst for power. By kidnapping someone with a special ability or knowledge, like a powerful Force - user or a brilliant scientist, he could gain an edge in his quest to rule the galaxy. For example, if he kidnapped a Jedi who knew the location of ancient Sith artifacts, he could use those artifacts to increase his own strength.
Another motive could be related to her family. Maybe there was some sort of blood feud or an old grudge against the Grangers. The kidnappers could have thought that by taking Hermione, they could get revenge on her family. In some fanfictions, there are secret magical families that have long - standing rivalries, and Hermione's kidnapping could be part of that.
Another reason might be revenge. There could be a character who has a grudge against Inuyasha or someone close to him. So, they kidnap him to make him suffer or to use him as bait to draw out his friends. For example, if there was a demon whose family was slain by Inuyasha in the past, they might kidnap him for revenge.
One possible motive could be for a prank. People might want to give their friends or family a big scare and then have a good laugh about it later. For example, like the stories where friends plan a fake abduction to surprise the victim with a party or some other fun event.
One possible motive could be his fear of losing her. In the Star Wars universe, Anakin is deeply in love with Padme. If in fanfiction he feels that she is in danger or might be taken away from him by some external force or person, his desperation could lead him to kidnap her in an attempt to keep her safe. For example, if he suspects the Jedi Council of having some secret plan regarding Padme, his unstable state of mind might push him to this extreme action.
Well, Ursula could kidnap Ariel in fanfiction because she wants to take Ariel's place. Think about it. Ariel has a loving family, a great voice, and is adored by many. Ursula, on the other hand, is often shunned. So she might think that by kidnapping Ariel and getting rid of her, she can step into Ariel's life. Maybe she wants to be the one who is loved by Prince Eric. Or perhaps she wants to be the favorite daughter of King Triton. It's all about her twisted desires for a different kind of life.
It could be that Peter has some sort of knowledge or information that the kidnappers want. For example, he might have accidentally witnessed a crime and the criminals want to keep him silent.
Maybe Rowle is under the orders of a more powerful dark wizard. In the world of Harry Potter, there are always those higher - ups in the dark side who might want Hermione for her knowledge of magic, especially things like ancient spells and magic theory. So Rowle could be tasked with kidnapping her for that purpose.