Daenerys Targaryen also appears frequently. In some fanfictions, she might be a key figure in helping the good king, perhaps through her military might or her experience in dealing with different cultures. Her dragons can also add an exciting element to the story.
Obviously, the King Beyond the Wall himself is a central character. He's often depicted as a strong and fearless leader. Then there are the wildlings who follow him. Characters like Ygritte are also quite common, as she was an important figure among the wildlings in the original series. And sometimes, characters from the Night's Watch get involved too, as they are in direct conflict or potential alliance with the King Beyond the Wall.
Daenerys Targaryen is often a main character. Since Dragonstone was an important place for the Targaryens, many fanfictions revolve around her connection to it. She might be exploring the secrets of the place or using it as a base for her conquests.
Brienne of Tarth is a character that can be paired with Jon Snow in fanfictions. Brienne is known for her loyalty and honor. She could serve as Jon's knight, protecting him and upholding justice in his kingdom. Also, Gilly could be part of the story. As Samwell Tarly's love interest and a person with knowledge from the far North, she could provide insights into the common people's needs and also help in matters related to the Night's Watch or the North in general.
Deidara is the most obvious one. Since he is the main user of explosive clay in the Naruto series, he often features prominently in such fanfictions. His unique art - based combat style makes for interesting storylines.
Bran Stark is definitely one of the most popular warg characters in 'Game of Thrones' fanfictions. His journey in the original series as he discovers and hones his warg abilities gives fanfiction writers a lot to work with. He can be placed in all sorts of different scenarios, such as using his warg powers to prevent the fall of Winterfell much earlier or having more direct confrontations with the Night King through his warging.
Jon Snow is often a popular choice. His skills in combat and his complex backstory make him an interesting character to include in a tournament setting. He could be fighting for honor or to prove himself.
Sansa Stark could also be paired with the prince. Sansa's knowledge of the North and her diplomatic skills could complement the prince's own abilities. Their relationship could be a slow - burn one, starting from mutual distrust to a strong alliance as they face common enemies in the fanfiction.
Another character she could be paired with is Arya Stark. They could form a sisterly bond that is stronger than in the original story. In the fanfiction, they might go on a quest to avenge their family or uncover secrets about their house that were long buried. This would make for an interesting story as they both have strong and distinct personalities.
Obviously, the Dragon King himself is a main character. He is usually depicted as a powerful and complex figure, with his own goals and desires for the kingdoms. Daenerys Targaryen is also often present, either as an ally or a rival to the Dragon King, given her own connection to dragons in the original series.
Arya Stark is also a common character paired with the Winter King in fanfiction. Arya's skills as an assassin could be useful to the Winter King's cause. She might be sent on secret missions by him or they could form a bond over protecting the innocent in the North.