Gilgamesh could be a powerful ally for one of the kings. Let's say he sides with Robb Stark. His incredible strength and battle prowess would turn the tides in many of Robb's battles. He could also use his influence to bring in other forces from outside Westeros. His presence would not only change the military situation but also the political one. Other houses would be forced to reevaluate their strategies and alliances, as they would now be facing a combined force of Robb Stark and the mighty Gilgamesh.
Rome could play the role of a mysterious foreign power. It might send envoys to the Seven Kingdoms to form alliances or gather information. This would add an extra layer of diplomatic intrigue to the story.
She could be a healer. With her knowledge of medical ninjutsu, she could save many lives in the war - torn Westeros. This would make her a valuable asset to any side she chooses to support.
He could be a heroic figure. For example, he could be like a knight - errant, traveling around Westeros and helping those in need. His swordsmanship, which is quite different from the traditional Westerosi style, would make him a unique combatant.
Wolverine might be a disruptor in the Game of Thrones world. He doesn't follow the same rules as the Westerosi. His presence could change the way battles are fought. For example, in a large - scale battle like the Battle of the Bastards, his individual combat skills could turn the tide. He could cut through enemy lines with his claws and inspire the troops he's fighting alongside. He might also be a voice of reason among the power - hungry lords, as he has his own sense of right and wrong that is different from the political games in Westeros.
A professional army could act as a protector. For instance, they could safeguard a small town or a noble family from bandits or rival houses. They would be more reliable than a conscripted or mercenary force.
Hashirama might become a powerful ally or a feared enemy in the Game of Thrones fanfiction. If he aligns himself with a certain house, his powers would make that house very difficult to defeat. He could also be a lone wanderer, using his skills to help the common folk. For instance, he could use his wood - style jutsu to create shelters for the poor or to clear paths in the forest for travelers. He would be like a force of nature in the world of Westeros, disrupting the normal power dynamics.
He could be a rebel. Tired of the Bolton family's traditional ways, he might try to change the family's reputation. He could be a force for good in the North, protecting the smallfolk from the usual Bolton brutality.
In a Game of Thrones fanfic, Hermione could be a mediator. There are so many conflicts in Westeros, from the Stark - Lannister feud to the battles for the Iron Throne. Hermione, with her logical mind and ability to see different perspectives, could step in and try to broker peace deals. She would use her communication skills, honed in the wizarding world, to get the warring parties to at least listen to each other and consider alternatives to all - out war.
Smaug could be a terrifying and powerful antagonist. He could be lured to Westeros by the smell of gold and riches in the various kingdoms. His ability to fly and breathe fire would make him a formidable foe against any army or dragonriders in the Game of Thrones universe.
He could play the role of a master strategist. Thrawn's ability to analyze his opponents and predict their moves would make him a valuable asset to any side in the 'Game of Thrones' power struggles. He could be the one to turn the tides in battles and sieges.