One possible alternate storyline could be that Robert manages to uncover the truth about Cersei's infidelity earlier. This would lead to a major political upheaval in King's Landing. He might exile Cersei and her children, which would change the power dynamics completely. With no Lannister influence at court, Ned Stark might have more sway, and the events leading to the War of the Five Kings could be averted.
It could be a really wild and unexpected crossover. Maybe Harry would have a penchant for the political intrigue and power plays of Game of Thrones.
One possibility could be the rebuilding of Westeros. After all the destruction and power struggles, the remaining kingdoms might focus on restoring their lands, economies, and populations. New leaders could emerge who are more interested in peace and cooperation rather than conquest.
Well, Goku could enter the Game of Thrones world during one of his training sessions where he accidentally travels through dimensions. In this new world, he would find the concept of the Iron Throne and the power struggle very strange. But his nature would make him oppose tyrants like Joffrey. He might start his own 'Saiyan - style' kingdom where strength and honor are the main values. His interactions with characters like Tyrion would be interesting, as Tyrion is a smart strategist and could potentially learn from Goku's combat skills while Goku could learn about the complex politics from Tyrion.
One great alternate history 'Game of Thrones' fanfiction is 'The Dragon's Return'. It imagines a world where the Targaryens never lost their power and how different the Seven Kingdoms would be. The story is full of political intrigue and detailed descriptions of a Targaryen - dominated Westeros.
One idea could be a fanfiction where Robert Baratheon's son, perhaps Joffrey (even though he was a cruel character), has a change of heart. In this fanfic, he could start to see the error of his ways after meeting a wise old maester who tells him tales of great but just kings. He then tries to make amends for his past actions, which would be a huge departure from his original character arc in the show and books.
Maybe in the fanfiction, his excessive pride got in the way. He was so confident in his military might from his past victories that he underestimated the threats within his own kingdom. This led him to be complacent, and when the challenges arose, he was ill - equipped to handle them.
One possible fanfiction could start with Robert Baratheon as a young man. He is full of ambition and dreams of a united Westeros under his rule. He trains hard in combat, his sword becoming an extension of himself. He meets his future friends, like Ned Stark, during these formative years. They share tales around the campfire and make grand plans for the future. As he grows older, he participates in battles, his victories making him more and more renowned. His charisma draws people to him, and soon he is seen as a natural leader. But with power also comes temptation, and he has to face the challenges of politics and intrigue that come his way.
In this fanfiction, a great storyline could be that Naruto and Joramun are seen as prophets or saviors by a small group of people in Westeros who are tired of the constant war and power struggles. They try to spread their message of peace and cooperation, but are opposed by the major houses who see them as a threat to their power. As they journey through Westeros, they also discover secrets about the land that could change everything. Maybe there are ancient powers that Naruto's chakra can interact with, and Joramun has some knowledge about these from his own world. This would create a complex and exciting story full of twists and turns.
Imagine Iron Man arriving in Westeros during the White Walker invasion. His repulsor rays and energy shields could be extremely effective against the undead. He could also use his technology to communicate over long distances and coordinate the defense of the Seven Kingdoms. His presence would surely disrupt the existing political and military order in the Game of Thrones world.
The merging could happen with a common enemy. Suppose there's an alien - like threat that starts to invade Westeros. Master Chief, being a hero used to fighting off extraterrestrial foes, steps in to help. His military tactics and combat skills would be a huge asset. He could train the soldiers in Westeros in new forms of warfare, and in the process, he'd have to navigate the complex political and cultural landscape of the Seven Kingdoms.