Maybe Lelouch is reborn as a noble in Westeros. He then uses his knowledge from his past life and his Geass ability to play the political game. He could be the one to expose the true nature of the White Walkers and use the situation to gain more power and influence, all while trying to keep his Geass a secret from those who might use it against him.
One possible plot could be Lelouch using his Geass power to manipulate the power - hungry lords in Westeros. He might start by influencing the Lannisters, creating chaos within their ranks and using their downfall to his advantage, perhaps to gain a hold on the Iron Throne.
A plot could involve Lelouch arriving in Westeros and allying himself with Daenerys Targaryen. He could use his strategic mind and Geass to help her in her conquest, but also have his own hidden motives. For example, he might plan to use her dragons to take over once she has defeated the other major players in the game of thrones.
A cool plot could be that Godzilla is lured to Westeros by the magic of the dragons. The dragons' power somehow calls to Godzilla across different dimensions or something. And then, once Godzilla arrives, it starts causing chaos. The different houses have to put aside their feuds and figure out a way to deal with this giant monster.
An interesting plot could be that the Stark family discovers a portal to the Naruto universe. Sansa Stark, being the politically astute character she is, tries to learn about the power structures in the ninja world. Meanwhile, Naruto and his friends are intrigued by the Starks' noble demeanor. They form an alliance to fight a common enemy that somehow threatens both their worlds, like a powerful dark force that has the ability to manipulate time and space.
An interesting plot could be that Naruto is transported to the world of Game of Thrones through some kind of magical portal. He quickly becomes involved in the power struggles as he tries to find a way back home. Along the way, he meets various female characters who are drawn to his courage and his strange powers. These women form a harem around him, and Naruto has to balance his relationships with them while also trying not to get caught up in the deadly Game of Thrones politics.
A plot where Deadpool somehow becomes a king would be really interesting. He'd probably run the kingdom in the most unorthodox way, making strange laws and having his own brand of 'justice'. For example, instead of beheading traitors, he might make them do stand - up comedy about their crimes.
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.
The more noble characters might initially be skeptical of Lelouch. They would see his methods as underhanded, especially if he used his Geass to manipulate. But as time went on and they saw the results of his actions, like uniting kingdoms against a common threat or bringing about a more just rule, they might come to respect him in a way, albeit grudgingly.
Perhaps a plot where the Dragonborn discovers an ancient power in Westeros that is related to their own Dragonborn abilities. They go on a quest to unlock this power, all while being hunted by various groups who either fear their power or want to use it for themselves. Along the way, they form unexpected alliances with characters from Game of Thrones, like a wildling or a maester. Their journey could take them to the far reaches of Westeros, from the Wall to Dorne, and they would have to adapt to the different cultures and challenges they face.
A possible plot could be that Naruto arrives in Westeros during a time of great turmoil, like the War of the Five Kings. His op abilities would make him a valuable asset to different sides. However, he would also face challenges as his values of friendship and loyalty might not be fully understood. He could try to form his own group of allies, made up of both the common people and some of the more honorable knights, to fight against the tyranny and power - hungry lords. His powers would be used to turn the tide of battles, but the political web would still be difficult for him to navigate.
The plot could center around a powerful artifact. In 'Game of Thrones', there are many powerful items like Valyrian steel swords. Suppose one such sword gets transported to the Marvel universe. Iron Man, being curious about new technology (even if it's more of a magical item in this case), starts to study it. This attracts the attention of both heroes and villains. Meanwhile, the character who owned the sword in 'Game of Thrones', say, Brienne of Tarth, travels to the Marvel universe to retrieve it. She teams up with Captain America, who admires her sense of honor. Together, they face off against villains like Loki, who wants to use the sword's power to take over the world.
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.