One idea could be exploring the origin of Lightbringer in more depth. Maybe it was created by an ancient civilization long before the events of 'Game of Thrones'. Another could be a story where a new character discovers Lightbringer and has to learn how to control its power without succumbing to its dark influence.
Daenerys Targaryen would be fascinating. She has her own dragons, but Lightbringer could be the key to truly uniting the people of Westeros under her rule. It could symbolize her rightful claim to the Iron Throne and be a tool to overcome any remaining opposition.
One idea could be exploring what would happen if Jon Snow was raised by the Starks as a trueborn son. Another could be a fanfiction about Daenerys Targaryen's journey if she had made different alliances earlier. Or perhaps a story about Arya Stark training with a different master assassin.
A great idea for 'Game of Thrones fanfiction' is to rewrite the story from the perspective of the smallfolk. For instance, how did they really feel during all the wars and power struggles? How did the common people in King's Landing cope with the different rulers? You could also explore a fanfiction where the White Walkers are not the villains. What if there was a misunderstanding and they were actually trying to protect the realm from some other greater threat?
One idea could be exploring what would happen if a minor character, like Gendry, had a more prominent role in the story. He could potentially become a powerful lord and change the political landscape.
One idea could be exploring what would happen if a minor character like Gendry had been secretly trained in magic. He could use his newfound powers to unite the smallfolk against the warring nobles. Another plot could revolve around a female knight from the North who disguises herself as a man to fight in the wars, and along the way, she discovers secrets about the White Walkers that no one else knows. Or perhaps a fanfiction where Daenerys and Sansa form an alliance much earlier and together they reshape the power dynamics of Westeros.
Another interesting concept for 'Game of Thrones' tragedy fanfiction is to focus on Daenerys Targaryen's madness. What if her decent into madness was more gradual and was caused not just by the loss of her dragons and Jorah, but also by a series of betrayals from within her own camp? You could write about how she started to see enemies everywhere and made decisions that alienated her from the people she was trying to liberate.
Well, for a 'Game of Thrones reincarnation fanfiction', you might consider having Arya Stark reincarnated as a sellsword. She could still retain her skills from her past life, like her ability to change faces and her combat skills. This new Arya could then get involved in various wars and power struggles across Westeros. Also, Jon Snow could be reincarnated in a world where the White Walkers have already won. He has to figure out a way to reverse the situation, using his past knowledge and leadership skills. And Cersei Lannister could be reincarnated as a maester's apprentice, which would give her a whole new perspective on power and politics.
One idea could be exploring what would happen if a minor character, like Gendry, had a more central role in the fight against the White Walkers. He could lead a group of common folk and prove that the power doesn't always lie with the nobles.
Well, you could have a fanfiction where a young character discovers they are a summoner. They start off by accidentally summoning small creatures like ravens or mice, but as they grow in power, they can summon dragons that are not related to the Targaryens. This new type of dragon could have different abilities, like breathing fire that can turn into ice. They then use these dragons to influence the power struggle in Westeros.
One idea could be Loki somehow being transported to the world of Game of Thrones and using his magic to manipulate the political intrigue. He might side with a particular house and use his wits to outsmart their enemies.