Well, a really common one is the idea of Erza from Fairy Tail taking on the role of a knight in the Game of Thrones universe. Her combat skills and strong sense of justice would make her a great addition to any side. Also, the concept of the dragons in Fairy Tail having some sort of connection to the dragon legends in Game of Thrones. Maybe they could even interact with Daenerys' dragons. And then there's the idea of the Fairy Tail characters having to navigate the complex social hierarchies in Westeros, which could lead to some really interesting stories.
One popular crossover idea is the characters from Fairy Tail facing the political intrigue of Westeros like in Game of Thrones. For example, Natsu could find himself in the middle of a power struggle for the Iron Throne. Another is having the magic from Fairy Tail being introduced to the world of Game of Thrones, which would completely change the dynamics of battles and power plays. And some might imagine the guilds in Fairy Tail getting involved in the wars between the different houses in Westeros.
One popular idea is a battle royale - where the powerful characters from Naruto and Fairy Tail compete. Another is a team - up against a common, super - powerful enemy. For example, Naruto's Rasengan combined with Natsu's Fire Dragon's Roar could be a really cool and powerful attack.
A common trope is the team - up against a powerful villain. This could be a super - strong demon from Fairy Tail's lore combined with an evil force from Dragon Ball Z. The heroes from both series then have to put aside their differences and work together. Also, the 'rivalry' trope is often used. For instance, Natsu and Goku might start off as rivals, competing to see who is stronger, but then they realize they need to work together. And of course, there's the 'training' trope, where characters from one series train the characters from the other series in their respective fighting styles.
One idea could be a story where Naruto characters are transported to the Fairy Tail world. For example, Naruto himself could end up in Magnolia and join the Fairy Tail guild. He might use his ninja skills in combination with magic, creating unique combat styles. His Rasengan could be enhanced with magical elements, leading to new and powerful attacks.
One interesting plot could be the mages from Fairy Tail being transported to the world of Game of Thrones. They might use their magic to deal with the political intrigue and battles there. For example, Natsu could use his fire magic to fight against the White Walkers, adding a new element to the fight against the undead.
Often, there are fanfictions where the worlds of Fairy Tail and One Piece start to merge. The islands in the One Piece world might start to have magical properties and the Fairy Tail guild could have to deal with the chaos of the pirates suddenly showing up in their world. This can lead to some really interesting character interactions, like Erza trying to discipline Zoro or Lucy befriending Nami and sharing their knowledge about different types of treasures.
A possible fanfiction could involve the creation of a new magic system in Westeros that combines the dark and mysterious nature of the Rinnegan with the existing magic in 'Game of Thrones'. For example, the White Walkers could be somehow related to the Rinnegan powers. Maybe the Night King was once a normal man who was experimented on with Rinnegan - inspired magic, which turned him into the powerful and terrifying being he is now. This would add a whole new layer of mystery and danger to the fight against the White Walkers.
One interesting crossover idea could be a battle tournament where characters from both Bleach and Fairy Tail participate. For example, Ichigo from Bleach could face off against Natsu from Fairy Tail. Their different fighting styles, with Ichigo's zanpakuto and Natsu's dragon slayer magic, would make for an exciting showdown. Another idea could be a team - up scenario. Maybe some of the Soul Reapers and Fairy Tail mages have to work together to defeat a common, powerful enemy. This would allow for interactions between characters who have different powers and personalities, like Rukia and Lucy. They could learn from each other's magic systems and grow as characters during the adventure.
Well, Daenerys Targaryen is often a popular choice. Her dragons and her journey of reclaiming the Iron Throne can be easily adapted into crossovers. For example, if she were to cross into a world full of magic - users, how would she use her power? Also, Jaime Lannister is quite popular. His character arc from a seemingly villainous knight to a more complex figure can be explored in different settings. In a crossover with a historical setting, his knightly skills and code of honor (or lack thereof at times) would be very interesting to play with.
Cersei Lannister could also be a popular choice. Her cunning and thirst for power in Game of Thrones could be enhanced in the Overlord fanfiction world. She could use her wits and the resources of the Lannisters to become a powerful Overlord - like figure, perhaps even making deals with the dark forces often associated with the Overlord concept.
Well, some might argue that Aegon Targaryen with his dragon in Game of Thrones would be very powerful. But if we consider Fairy Tail, Acnologia, the dragon king, would be extremely powerful. If he were to enter the Game of Thrones world, he could easily destroy entire armies and fortresses with his dragon powers.