Perhaps Dwight Enys from Poldark and Arya Stark from Game of Thrones. Dwight is a healer and a man of science in his world, while Arya is a trained assassin. The idea of them coming together, with Arya maybe getting some medical help from Dwight or Dwight learning some of Arya's survival skills, would be quite unexpected and could lead to a unique fanfiction plot.
Definitely Cortana and Tyrion Lannister. Cortana is highly intelligent and has access to a vast amount of knowledge. Tyrion is known for his wits. They could form an alliance where Cortana provides strategic advice based on her analysis, and Tyrion uses his political acumen to make things happen. Their conversations would be really fascinating as they come from such different worlds but are both very clever.
Hot Pie could be the unexpected hero. He might use his baking skills in an unexpected way. For instance, he creates a special type of bread that has some sort of magical property. This bread could be used to heal the wounded or even give the soldiers who eat it superhuman strength during a battle against a powerful enemy.
How about Hot Pie? He's a simple baker boy. But imagine if he somehow stumbled upon a dragon egg and became a rider. His journey from baking pies to riding a dragon would be full of comical and also heart - warming moments as he tries to fit into the world of dragon riders.
I think Voldemort and Fluttershy would be a really unexpected pairing. Voldemort is all about power and darkness, while Fluttershy is the shy and gentle pony. It would be very strange to see how they interact if they were in the same story.
One interesting crossover could be the comparison of the power struggles. In Poldark, there are battles over land and mining rights, much like in Game of Thrones where houses fight for the Iron Throne. Characters from both might interact in a fanfiction, for example, Ross Poldark could meet Jon Snow. They could share their experiences of leading and fighting for what they believe is right. Ross with his fight for the Cornish people and Jon with his fight against the White Walkers.
Solaire from Dark Souls and the Hunter from Bloodborne could make an interesting pair. Solaire is known for his sunny disposition and quest for his own sun, while the Hunter is all about the hunt in the dark and gothic world of Bloodborne. Their different outlooks and skills could lead to some great character development as they face challenges together.
It could be Jon Snow. If he has a Stand in the fanfiction, combined with his already proven leadership skills and combat abilities, he would be a force to be reckoned with. His ability to come back from the dead might also be related to his Stand powers in some way, making him even more formidable.
Charlotte and Trip would be quite the pair. Charlotte is the smart and level - headed friend in Henry Danger. Trip is the fun - loving and somewhat scatterbrained member of the Game Shakers crew. Their personalities are so different that it would create a lot of humorous and interesting interactions. Charlotte could help Trip focus on important tasks, while Trip could introduce Charlotte to a more laid - back and creative way of thinking.
One interesting pairing could be Jasper from Henry Danger and Kenzie from Game Shakers. Jasper is often the comical sidekick in Henry Danger, and Kenzie is really smart and business - minded in Game Shakers. Their interactions would be really funny as Jasper might do some silly things that Kenzie would have to correct or find a way to work around. At the same time, Jasper could bring out a more laid - back side of Kenzie, and they could develop a unique friendship while working on whatever adventure or project comes their way in the crossover.
One of the most popular assassin characters in Game of Thrones fanfiction is Arya Stark. In the original series, Arya has assassin - like training in Braavos. In fanfiction, her skills are often enhanced and she is sent on all kinds of secret and dangerous missions. Another could be Jaqen H'ghar. His mysterious nature and assassin skills make him a fascinating character to explore further in fanfiction. He can change his face, which adds an extra layer of intrigue to his character in fan - made stories.