There's a fanfic called 'Sister's Bond'. In this story, the sister is brought into their lives in a rather mysterious way. It shows how she struggles to adapt to the life of hunting monsters while also trying to understand her new - found brothers. It's full of action and some really heartfelt moments between the siblings.
In a fanfiction, their sister could be a prophet. She starts having visions that lead the boys to new cases. But there are forces that want to use her for their own gain. Sam and Dean would have to fight not only the regular demons and ghosts but also those who are after their sister.
One common theme is family loyalty. Sam and his sister's bond is often explored, showing how they would do anything to protect each other. Another theme is the struggle with the supernatural world. Just like Sam and Dean in the show, the sister also has to face demons, ghosts, and other creatures. And self - discovery is also a theme, as the sister may find out new things about herself, like hidden powers or a different origin.
The main reason is that it adds a new dynamic to the existing relationship between Sam and Dean. A sister character can bring in a whole new set of emotions and storylines. For example, it could be about protecting their sister, or the sister protecting them in a different way than they are used to.
She could be a nephilim, half - angel and half - human. This would put her in great danger as both angels and demons would be after her. Sam and Dean would have to constantly protect her and figure out a way to keep her powers in check.
One common theme is family. Since Sam has a twin sister in these fanfictions, it often explores their family bond, how they support or sometimes conflict with each other. Another theme is the supernatural world. The sister usually has to navigate the same world of demons, angels, and monsters as Sam.
Well, I really like 'Sister of Sam: The Hunter's Kin'. In this fanfiction, Sam's sister is a strong - willed character who is determined to prove herself in the hunting community. It has some great action scenes and emotional moments between the siblings. Another good one is 'The Protective Sister', which shows how Sam's sister is always looking out for him, even when he doesn't realize it. And 'Sam and His Sister: Supernatural Allies' is about how they team up with other hunters to take on a major threat to the supernatural world.
Obviously, Dean and Sam are main characters. They are the protective older brothers. And then there's the baby sister, who is likely a central figure as well, with her own personality and role in the fanfiction. There might also be other recurring characters from the 'Supernatural' universe like Castiel who could play important parts in the story.
Well, there's 'Sam's Twin Sister: A New Chapter'. This fanfiction takes a different turn by making the sister a key player in an ancient prophecy. It's full of action and emotional moments. Also, 'Twin Sister's Impact' is worth checking out. It focuses on how the sister's presence changes the dynamics of Sam's relationships with Dean and other characters in the Supernatural world.
In fanfiction, if Sam was kidnapped, it could lead to a very intense story. Dean would surely go on a rampage to find him. Maybe Sam was kidnapped by a powerful demon who wants to use him for some dark ritual. It could also be a new, unknown enemy who has a vendetta against the Winchesters.