Well, Katherine might use her seductive powers to gain influence. She could target powerful men like Joffrey or Ramsay, and then manipulate them to do her bidding. But she'd also have to be careful as the people in Game of Thrones are not easily fooled. If she were to target someone like Tyrion, he'd likely see through her schemes quickly. So she'd need to be very strategic in her approach. Also, she might be interested in the magic in the Game of Thrones world, like the Red Priests' magic, and try to learn it for her own advantage.
She could fit in as a spy. Given her ability to deceive and her immortality, she could gather information for different factions. For instance, she could work for the Starks initially, but then switch sides if she saw more benefit elsewhere.
Katherine Pierce in a Game of Thrones fanfiction could be a wild card. She could start by infiltrating one of the great houses, perhaps the Lannisters. She'd likely try to play the family members against each other, using her knowledge of human nature and manipulation. Her presence would surely disrupt the balance of power in King's Landing. And she might even find herself falling for one of the dashing knights or lords, only to use him as a pawn in her grand scheme for power.
The Hulk might be seen as a sort of monster in the context of Game of Thrones. Just like how they have direwolves and dragons, the Hulk could be another mythical - but in this case, suddenly very real - creature. He could be shunned by some and perhaps worshipped as a god by others, depending on how different regions of Westeros react to his existence.
In fanfiction, Aragorn could potentially be a king from a far - off land who arrives in Westeros. He might bring with him a different style of leadership and a sense of honor that is somewhat different from the lords and ladies of Westeros. He could get caught up in the power struggles, especially if he realizes the threat of the Iron Throne being misused. Maybe he would try to form alliances with the more noble houses to bring stability to the land.
They could be a new faction. Samurai have a strict code of honor, much like the knights in Westeros. They might be seen as a threat initially, but could also form alliances. For example, they could side with the Starks who also value honor. Their unique fighting styles would be a novelty in the battles of Westeros.
A house gardener could fit in as a keeper of secrets. The gardens often have hidden corners and old trees that could hide things. He might stumble upon a hidden cache of weapons or a secret meeting place. His presence is often overlooked as he is just a gardener, so he can observe a lot without being suspected.
Percy Jackson would be a very interesting addition to the Game of Thrones world. His ability to control water would be a huge asset in battles. For instance, he could create floods to stop enemy armies or use water to put out dragon fire. In the political arena, he might be seen as a threat by some because of his powers, but also as a potential ally by others who want to use his abilities for their own gain.
Kakashi could fit in as a foreign warrior. He could bring his ninja techniques which would seem like magic to the people of Westeros. His stealth and combat skills would make him a valuable asset or a feared opponent in the battles and power plays of the Seven Kingdoms.
Smaug could potentially be a part of the magical elements in the 'Game of Thrones' fanfiction. He could be connected to the old magic that once existed in Westeros. Maybe his presence awakens other dormant magical forces. His actions could also influence the political landscape. For example, if he attacks a certain region, the lords there would have to divert their resources from the power struggles to deal with the dragon threat, which in turn could give an advantage to other houses.
Legolas could be an outcast in the Game of Thrones world at first. But as he gets to know the people and their struggles, he decides to get involved. He could start a new movement, based on elven values like harmony with nature and loyalty. His actions could inspire characters like Jon Snow to think differently about leadership and ruling, and together they could work towards a more just and sustainable Westeros.
Achilles would be an out - of - place yet fascinating addition to the Game of Thrones universe. Given his near - invincibility in battle, he could potentially change the balance of power. For example, if he fought for the Unsullied, they would become an even more terrifying military force. However, his sense of honor and heroism might clash with the more cut - throat politics of Westeros.