Perhaps the Urgals from the Inheritance Cycle invade Westeros. Their brute strength and different culture would disrupt the balance of power. The different houses in Westeros would have to put aside their differences to fight this new threat. And a character like Jon Snow could learn about the Urgals' way of fighting and use that knowledge to his advantage in future battles.
One interesting plot idea could be exploring a new magical inheritance that is discovered in the wizarding world. For example, a long - lost spellcasting ability that only certain descendants of an ancient wizarding family can possess. This could lead to a whole new adventure for the characters as they try to understand and master this new inheritance.
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.
One idea could be exploring a new dragon rider from a different land in the Inheritance Cycle world. They could have a unique bond with their dragon, perhaps a dragon with a rare color or ability. Another plot could involve a mystery within the ancient dragon lore that the main character of the fanfic has to uncover.
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.
A really cool 'Game of Thrones fanfiction' plot could involve the resurrection of some of the dead characters in a different way. For example, what if Ned Stark was brought back not as a vengeful wraith but as a wise advisor to a new king or queen? His honor and wisdom could shape the future of Westeros in a completely new direction. And it would be interesting to see how the other characters react to his return.
Perhaps a fanfiction where Daenerys Targaryen lands in Westeros earlier and forms an alliance with the Starks before the events of the main series. This would completely shift the political landscape and the fight for the Iron Throne. She could bring her dragons to help fight the White Walkers from the start.
One idea could be a fanfiction where a gamer gets transported into the world of the Inheritance Cycle. They could use their gaming knowledge to navigate the magical and dangerous world, like knowing strategies from RPGs to deal with dragons. Maybe they form alliances with characters in the story in unexpected ways, bringing a fresh perspective to the Inheritance Cycle universe.
One idea could be exploring a long - lost inheritance of a minor character. For example, Neville could discover that his family has an ancient magic related to plant communication that was lost over the years. This could add a new dimension to his character and his role in the wizarding world.
One idea could be that Oliver Queen somehow gets transported to Westeros. He could use his archery skills to survive in the dangerous world. Maybe he'd join a faction, like the Night's Watch, and teach them his modern combat techniques.
One idea could be exploring what would happen if a minor character, like Gendry, became the King of Westeros. He has a claim to the throne through his Baratheon blood and his time with the Brotherhood without Banners could give him a different perspective on ruling. Another plot could involve a female character, like Brienne, leading a new order of knights that are dedicated to protecting the realm in a more democratic way. Or perhaps a story where the White Walkers and the humans form an uneasy alliance against a new, even greater threat from Essos.