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.
One possible motive could be power. By stealing Ariel, Ursula might have planned to use her as a bargaining chip with King Triton. Ariel was Triton's beloved daughter, and Ursula could have demanded something in return for Ariel's freedom, like control over part of the ocean or some powerful magical items.
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.
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.
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.
A different way to develop their relationship could be through a magical accident. Let's say a spell backfires and Ariel and Ursula's minds are swapped. They have to live in each other's shoes for a while. Ariel experiences Ursula's loneliness and the reasons behind her actions, while Ursula gets a taste of Ariel's kind and curious nature. This could lead to a more empathetic relationship between them.
Well, obviously Ariel and Ursula are the main characters. Ariel is the curious and adventurous mermaid princess. She is known for her beautiful voice and her longing for the human world. Ursula, on the other hand, is the sea witch. She is often depicted as a villain, with her tentacles and her devious plans to take over the underwater kingdom or cause trouble for Ariel.
It's popular because their relationship in the original story is so complex. There's a lot of room for exploration. Fans like to imagine different scenarios where their dynamic can change, like friendship instead of enmity.
One possible motive could be that Sasuke is being controlled by some dark force. Maybe an enemy has a hold over him and is using him to kidnap Sakura as a way to get to Naruto or the Hidden Leaf Village. Another reason might be a misunderstanding on Sasuke's part. He could think that Sakura has some information that is crucial to his personal vendetta and decides to take her by force to get that information.
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.
Well, in some fanfictions, Bill might kidnap Will to gain more power. Maybe Will has some special ability or knowledge that Bill wants to use for his own evil plans.