Well, it could be one of the rivals of the empress or someone with a hidden agenda. Maybe it's related to power struggles or personal vendettas. But it really depends on the specific plot and characters of the manga.
Sam is also a probable candidate. Given her feisty nature, it could lead to some interesting scenarios where she tries to fight back against the kidnapper. And her relationship with Carly and Freddie would drive them to take action.
Papyrus can also be a victim of kidnapping in fanfictions. His naive and friendly nature makes him an easy target in some stories. His kidnapping could lead to Sans going on a desperate search for him, which would involve a lot of action and emotional moments as Sans tries to rescue his brother.
Judy Hopps is often a commonly kidnapped character. She's a central figure in Zootopia, so it makes sense that fanfiction writers would target her for a kidnapping plot. Her small size as a rabbit and her important role as a police officer could be factors that make her an appealing target in these stories.
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.
The empress in 'The Neverending Story' was Moon Child. Her identity is deeply intertwined with the fabric of the story. She is not just a character but a symbol of the beauty, magic, and hope within the world of Fantasia. Her very existence gives purpose to the journey of the main characters and her name, Moon Child, evokes a sense of celestial and pure beauty, which is very much in line with her role in the story.