In some fanfictions, Light might be kidnapped by someone who wants to reform him. For example, a person who believes that Light has gone too far with his Kira persona but still sees good in him. They could take him to a secluded place and try to make him see the error of his ways through various means like showing him the real impact of his actions on innocent people. This would lead to a very character - driven and psychological plot.
One possible plot could be that Light is kidnapped by a group who has discovered his identity as Kira and wants to expose him to the world. They hold him captive while they gather evidence. Another could be a rival Death Note user kidnaps Light to steal his Death Note and gain ultimate power. And perhaps a secret organization kidnaps him to study the power of the Death Note and how it has affected Light's mind.
Well, a really interesting fanfiction plot could be that Light is kidnapped by an otherworldly being. This being is intrigued by the power of the Death Note and wants to understand how a human like Light can wield such power. The kidnapper takes Light to a different dimension where the rules are different. Light has to use his wits not just with the Death Note but also to find a way back to his own world while dealing with this strange kidnapper.
Maybe Misa. She's completely devoted to Light, but what if she discovers that Light has been using her all along? In a fit of rage and heartbreak, she could kidnap him. She has the means as she's also involved with the Death Note. She might want to make Light pay for his betrayal or force him to love her truly.
One possible plot could be that Anakin is kidnapped by a secret Sith cult who wants to turn him fully to the dark side. They might use dark side magic to keep him imprisoned and try to manipulate his mind.
One possible plot could be that Sakura discovers a unique power within her blood that has been passed down through her family. This power could be related to healing, but with a twist. For example, it might be able to heal not just physical wounds, but also emotional traumas. However, this power comes at a cost, and she has to figure out how to control it without sacrificing her own well - being.
One plot could be Percy exploring his unique powers as the son of Oceanus. He might discover abilities that are different from the regular demigods. For example, he could have a special connection to the deeper parts of the ocean that no one else has.
One interesting plot could be that the werewolf kidnaps a human who has a special power that the werewolf pack needs. Maybe the human can heal the sick werewolves, and the werewolf kidnaps them to bring them back to the pack. Another plot might involve a werewolf kidnapping a human out of love. The werewolf has been observing the human for a long time and decides to take them away to protect them from the cruel human world. Or perhaps a werewolf kidnaps a human in a case of mistaken identity, thinking the human is someone who has wronged their pack in the past.
A really interesting plot could be that Sonic is kidnapped into another dimension by a powerful being. In this dimension, the laws of physics are different, and Sonic has to figure out how to use his speed in new ways to escape. His friends back in his own dimension are desperately trying to find a way to bring him back. Meanwhile, Sonic meets some strange new allies in this other dimension who help him in his quest to return home.
Another plot could be that she time travels to a future where something bad has happened to her family. She then has to figure out what went wrong in the present to cause this future and work on changing it. For instance, if in the future Klaus and Caroline are no longer together and their family is falling apart, she could go back and try to prevent the events that led to this.
Another plot could involve them traveling to a different timeline altogether. In this new timeline, they might find themselves in a world where the power of Geass doesn't exist. This would force them to rely on their wits and leadership skills in a completely different way. They could either try to find a way back to their original timeline or decide to make the best of the situation and change this new world for the better.
Some fanfictions focus on Light's relationships. For example, how his relationship with his family, especially his father, might have changed if things had gone differently. There could also be fanfictions that explore a romantic relationship for Light, which is quite different from his single - minded pursuit of his 'new world' in the original story.
Perhaps in a fanfiction, an enemy uses death magic to bring back powerful villains from Naruto's past. Naruto then has to use his own skills and newfound knowledge of death magic (maybe learned from a wise hermit) to defeat them all over again. This could lead to some really intense battles and character development for Naruto as he grapples with this new threat.