One great crossover could be the characters from Bleach having to navigate the complex political landscape of Westeros from Game of Thrones. For example, Ichigo could find himself in the middle of the power struggle between the Lannisters and the Starks. He might use his Soul Reaper powers to protect those he deems worthy, like Arya Stark. His sword skills would be a great asset in the battles of Westeros.
One interesting crossover could be the characters from Bleach having to navigate the political intrigue of Westeros in Game of Thrones. For example, Ichigo could be seen as a sort of 'outsider' knight, using his sword skills to protect the innocent in a land full of backstabbing nobles. His spiritual powers might be mistaken for some sort of dark magic at first.
Definitely Jon Snow. His leadership skills and sense of justice would fit well in the world of Arrow. He could team up with Oliver Queen and they could exchange ideas on leading their respective groups.
One interesting crossover could be the Avengers having to deal with the political intrigue of Westeros. For example, Iron Man might use his technology to try and outwit the various lords vying for the Iron Throne, much like he does with his corporate rivals. Another could be Thor interacting with the gods in the Game of Thrones universe, perhaps recognizing some similarities between their powers.
One great crossover could be a scenario where the dragons from 'Game of Thrones' are used in the battles of Middle - earth in 'Lotr'. For example, imagine Smaug - like dragons fighting alongside the orcs against the free peoples. Another interesting idea is to have characters from the two universes meet. Maybe Arya Stark could end up in Middle - earth and learn some of the elvish skills in combat and stealth. There could also be a crossover where the magic systems interact, like the wizards in 'Lotr' trying to understand the power of the White Walkers in 'Game of Thrones'.
One interesting crossover could be a scenario where the powerful vampires from The Originals find themselves in the political intrigue of Westeros from Game of Thrones. Maybe they get involved in the power struggles between the different houses, using their vampiric abilities to gain an edge. For example, Klaus Mikaelson could try to manipulate Cersei Lannister for his own ends.
A really cool fanfiction idea could be that the ancient prophecies in both Eragon and Game of Thrones are somehow related. Characters from both stories start to realize that their fates are intertwined due to these prophecies. This could lead to a grand adventure where they have to work together to fulfill or prevent the prophecies from coming true. For instance, Daenerys Targaryen and Eragon could join forces, with their dragons, to face a great evil that has been foretold in both of their worlds' prophecies.
A great crossover idea in the fanfiction could be the magic systems. Imagine Daenerys Targaryen learning about the Signs that Geralt uses. Her dragons could be intrigued by the magic of The Witcher world, and perhaps they could interact in ways that are both unexpected and exciting. This could lead to new alliances or battles depending on how the story unfolds.
One interesting crossover could be the use of Aquaman's underwater kingdom's politics and apply it to the power struggles in Game of Thrones. For example, the complex hierarchies and rivalries among different underwater tribes in Aquaman's world might mirror the Houses vying for the Iron Throne. Another could be a character from Game of Thrones finding themselves in Aquaman's world and having to adapt to the underwater environment and its rules.
One interesting crossover could be a scenario where the Mandalorian's combat skills are put to use in the political intrigue of Westeros. Maybe he's hired as a bodyguard for a powerful lord or lady, and his no - nonsense approach disrupts the usual scheming. For example, when faced with the Littlefinger - like characters, his straightforwardness would be a contrast to their devious ways.
One interesting crossover could be the combat styles. The Spartans' disciplined and fearless fighting in 'Spartan 300' could be incorporated into the battles of 'Game of Thrones'. For example, imagine the Unsullied being trained in Spartan - like combat formations. Another aspect could be the political intrigue. The complex power plays in 'Game of Thrones' combined with the Spartan's sense of honor and duty in their city - state politics.