Sometimes, Dean is taken hostage by a powerful demon who has a vendetta against the Winchesters. This can lead to a complex plot where Dean has to use his wits and any resources he has at his disposal to escape or hold out until Sam arrives. There might also be elements of Dean making deals or trying to outsmart the demon.
Sometimes, in these fanfictions, Dean is secretly married to a supernatural being. For example, he might be married to a fallen angel. This creates a whole new set of problems as he has to deal with the politics and power struggles within the supernatural world while keeping his marriage a secret from Sam and the rest of the hunting community. It can also lead to some interesting character development as Dean has to navigate his feelings for this other - worldly being and his loyalty to his family.
There are often plotlines where the reader is transported into the Supernatural universe and immediately runs into demon dean. Their relationship starts off rocky, with dean seeing the reader as an easy target or a nuisance. But as the story unfolds, they discover that they are linked in some way, perhaps by a prophecy or a shared past life. This leads to a journey of self - discovery for both of them as they figure out their relationship and their roles in the supernatural world.
A plotline could be that on Halloween, Sam and Dean discover a town where every year, people disappear mysteriously. They suspect it has something to do with an ancient Halloween ritual gone wrong. As they dig deeper, they find that a group of cultists are trying to summon a powerful entity. Sam uses his research skills to find a way to stop the summoning, while Dean prepares for a fight.
Another plot could be Dean falling in love with an angel. In the Supernatural world, relationships between hunters and angels are complex. So, a fanfiction might explore how Dean's tough hunter exterior softens as he falls for an angel, and how they navigate the differences between their two worlds.
You can try websites like Archive of Our Own (AO3). It has a large collection of fanfiction, including many about Dean in hostage situations in the Supernatural fandom. Just use the search function to look for relevant tags.
The trauma he has endured throughout his life is also a frequent theme. All the battles with demons, angels, and other supernatural beings have left their mark on him. In some fanfictions, he might cry when memories of past traumas resurface, like the time he was in Hell. It could be a moment of vulnerability where he can't hold back the tears any longer.
Friendship is a very common theme. Fans love to explore the unique bond between Charlie and Dean. Their friendship is different from Dean's relationships with other characters in the show, and fanfiction often delves into how they support and understand each other.
One common theme is mentorship. Dean often takes on a mentor - like role to Claire. For example, he teaches her how to hunt monsters more effectively.
One common theme is Dean's struggle with his vampiric nature. He's a hunter in the show, so becoming a vampire goes against everything he believes in. Fanfictions often explore how he deals with this internal conflict.
There are also a lot of emotional themes. For example, the idea of Dean having to protect Ben at all costs, or Ben trying to understand Dean's complex and often troubled past. These emotional elements add depth to the fanfictions and can make them really engaging.