Well, in a kidnapped fanfiction involving Pokemon Gold, perhaps the main character could be kidnapped by a rival trainer who wants to steal their rare Pokemon. This would lead to a series of events where the kidnapped character has to find a way to escape and protect their Pokemon at the same time.
One common theme is the struggle for freedom. The kidnapped character is constantly trying to break free from their captors. This often involves using their wits and the bond with their Pokemon.
Well, Team Flare might see Ash as a threat to their plans. By kidnapping him, they could prevent him from interfering in their evil schemes. They might keep him locked up in some secret base. Ash, being the determined trainer he is, would probably try to escape and find a way to defeat Team Flare from the inside. He could befriend some of the captive Pokemon in the base and use their help to break free.
Well, in fanfiction, if Thor kidnapped someone, it would be a huge deviation from his normal heroic character. It could be that he's trying to protect the person from a greater danger in his own, misguided way. Or perhaps he's been tricked into thinking the person has information vital to Asgard's safety. This situation would definitely shock his friends and allies, and would probably make for a very interesting and complex fanfiction story.
Well, in this kind of fanfiction, Sonic might be held in a strange and dangerous place. His friends like Tails would surely start a rescue mission. They could search all over the Sonic's world, facing various obstacles on the way. Maybe the kidnapper has some evil plan related to Sonic's speed or his Chaos Emeralds.
In a fanfiction like this, Bumblebee could be kidnapped by a powerful alien race that has a vendetta against the Autobots. The kidnappers might subject Bumblebee to various forms of torture to break his will. However, Bumblebee's strong spirit would keep him from giving in. His Autobot comrades would eventually come to his rescue, engaging in an epic battle against the kidnappers.
In this fanfiction, Ichigo might be held in a secret location by Aizen. Aizen could be planning to use Ichigo for some dark experiment or to gain his power. Maybe he'll try to manipulate Ichigo's Hollow side for his own evil purposes.
Well, in such a fanfiction, Sakura might be used as a bargaining chip. The Akatsuki could try to exchange her for something valuable, like secret jutsu. Or they might want to extract information from her about Konoha's defenses.
In this kind of fanfiction, Robin might be in a lot of danger. Slade could be using Robin to get to Batman. He might try to brainwash Robin and turn him against his friends. For example, he could lock Robin in a secret lair and show him false information about Batman to make Robin question his loyalty.
In the 'ichigo gets kidnapped fanfiction', he might be rescued by his friends. For example, his comrades from the Soul Society could sense his distress and come to his aid.
If Oscar is kidnapped in a fanfiction, his friends would be devastated. Ruby, being the leader, would immediately start planning a rescue. They might search for clues in the last place he was seen. Weiss could use her family's resources to try and track down any leads.