One interesting fanfiction could be about the Lich King's arrival in Westeros and how his powers of necromancy would disrupt the power balance. He might raise the dead from the many battlefields in Westeros, creating an undead army that would terrify the Seven Kingdoms. Another could be a story where the Lich King forms an alliance with a powerful Westerosi house, perhaps using his magic to help them gain the Iron Throne in exchange for something dark and sinister.
One interesting fanfiction could be where Jon Snow as king focuses on rebuilding Westeros after the long and brutal wars. He might use his unique experience of being both a Stark and a Targaryen to bring together the feuding houses. Another could be about his challenges in ruling, like dealing with the remaining White Walker threats in the far North that still lurk even after the big battle. There are also fanfictions that explore his relationships with other characters in a new light, such as his interactions with Daenerys' former followers as he tries to incorporate them into his new kingdom.
One interesting fanfiction could be one where a character discovers a long - lost magic in the Godswood. Maybe they find an ancient spell hidden among the roots of the heart trees. Another could be a story of love that blossoms in the Godswood, with two characters from different houses meeting secretly there.
One interesting fanfiction could be where the characters in 'Game of Thrones' discover guns from a foreign land. They might initially be confused by this strange new weapon. For example, Jon Snow could be one of the first to study how it works and try to incorporate it into the Night's Watch's defenses against the White Walkers. It would completely change the power dynamics in the Seven Kingdoms.
A great 'Game of Thrones' Balerion fanfiction could be centered around his relationship with other dragons. In the books and show, we don't get a lot of details about how the dragons interacted with each other on a deeper level. A fanfic could explore rivalries or alliances between Balerion and the other dragons. It could also show how Balerion's presence affected the behavior and growth of the younger dragons. This would add a whole new dimension to the dragon lore in the 'Game of Thrones' universe.
In some fanfics, the best crossovers involve the cultures clashing. The wildlings in Game of Thrones could be seen as similar to some of the undead - serving races in the Lich King's domain. A crossover could explore how they interact when the Lich King's influence starts seeping into Westeros. Another interesting idea is if the Red Priests' magic was a counter or a link to the Lich King's power. And a crossover where Tyrion Lannister has to use his wits to outmaneuver the Lich King's minions would also be quite engaging.
One interesting fanfiction could be one where Viserys Targaryen manages to escape his fateful end in the series. He might gather allies in Essos and build an army strong enough to actually take back the Iron Throne. This would show a different side of his character, more of a survivor and a strategic thinker rather than the impulsive and cruel figure we saw in the show.
One interesting fanfiction could be one where Robert Baratheon survives and has to face the challenges of ruling Westeros in a more peaceful way. He might have to deal with political intrigues without the use of brute force as much. Another could be a story about his youth, exploring his relationship with Ned Stark before all the chaos of the Iron Throne began. And there could also be a fanfic that focuses on his relationship with his children, had he been more involved in their upbringing.
One interesting fanfiction could be about Podrick's adventures beyond the events shown in the show. Maybe he travels to far - off lands and uses his skills learned in the Seven Kingdoms to survive and thrive. For example, he could end up in Essos and get involved in the power struggles there.
One interesting fanfiction could be about a character's journey under the moon's beauty in the Game of Thrones world. Maybe a young girl who discovers a hidden power while the moon is full and it changes her fate in the dangerous political and magical landscape of Westeros.
One type of fanfiction could be about Catelyn Stark's backstory that wasn't fully explored in the original series. It could show her growing up, her early days of marriage, and how she developed her strong will. Maybe it delves into her relationship with her family members before the events of the main story, like her parents and siblings, and how that influenced the person she became in Game of Thrones.