There are many ways fanfiction writers could incorporate Jon Snow and the Dark Sister. For example, the Dark Sister could be tied to Jon Snow's true heritage. Maybe it was hidden away waiting for him to claim it as a Targaryen. This could lead to new storylines where he uses the sword to fight against the White Walkers or in the battle for the Iron Throne.
One interpretation could be that the Dark Sister is a symbol of Jon Snow's destiny. It might be a sign that he is meant to play a much larger role in the world of Westeros. For instance, he could use it to unite the North and the South.
One possibility is that Jon Snow uses his new Faceless Man skills to infiltrate the Boltons' camp undetected. He could change his face to look like one of their soldiers and gather crucial intelligence for the Starks.
A great deal of Jon Snow and Iron Throne fanfictions focus on his relationships. For example, his relationship with Daenerys could be very different in fanfictions. In some, they rule together on the Iron Throne, combining their claims and powers. In others, they are at odds, with their relationship being a major obstacle in Jon's path to the throne. And of course, there are fanfictions where his Stark family ties also influence his actions regarding the Iron Throne, as loyalty to his family is a strong part of his character.
One possible plot could be that Jon Snow finds the Dark Sister in an ancient ruin in the North. He then has to learn to control its power to fight off a horde of undead that are immune to normal weapons.
One possibility could be that in the fanfiction, Jon Snow discovers the Valyrian steel in an ancient castle's armory. Maybe it was hidden away for centuries, and his discovery sets off a chain of events that changes the course of his journey.
Yes, there are quite a few. You can start by looking on fanfiction websites like Archive of Our Own. Just search for 'Jon Snow wields Dark Sister' and you'll find a variety of stories with different plotlines and interpretations.
It's interesting because it can explore different aspects of their characters. For example, how their relationship might change if they were in different situations, like facing a common enemy or having to make difficult decisions together. It gives a new perspective on their individual personalities as well.
You could also try searching on Tumblr. There are many bloggers who are into 'Game of Thrones' fanfiction and might have reblogged or even written their own dark and powerful Jon Snow stories. Use relevant tags like #JonSnowFanfiction #DarkJonSnow to narrow down your search.
There's also 'Sister's Devotion'. In this fanfiction, the author explores the emotional connection between Jon and his sister. It shows how their relationship evolves from a simple family bond to something much more profound, especially in the face of the various threats that lurk in the Seven Kingdoms.
One common theme is his struggle with new - found power. In these fanfictions, Jon Snow often has to deal with the moral implications of his power, whether it's a new magical ability or a political power. Another theme is his relationships. His interactions with other characters, like Sansa or Daenerys, can change significantly when he becomes dark and powerful.