One idea could be to explore his upbringing in a world where his mother has conquered Westeros. He could grow up with a strong sense of justice, influenced by Daenerys' ideals. Another could be his relationship with the dragons. Maybe he has a special bond with one of them that is different from his mother's.
A really interesting angle could be his struggle with his identity. He is the son of Daenerys, but he also has to carve out his own path. He might face opposition from some of the Westerosi lords who are wary of his mother's power. He could try to prove himself not just as Daenerys' son, but as a worthy leader in his own right. He might focus on building alliances with the smallfolk, understanding their needs better than the nobility, and through this, gain a loyal following that respects him for who he is rather than just for being Daenerys' heir.
A plot idea could involve Jon and Daenerys having to face a common enemy that is not the Night King. Suppose a new and powerful warlord rises in Essos and decides to invade Westeros. Jon and Daenerys would have to combine their forces, not just their military but also their diplomatic skills. Daenerys' experience with different cultures in Essos and Jon's knowledge of the North and the Seven Kingdoms would be put to the test as they try to form alliances against this new threat.
One idea could be an OC who is a healer from a far - off land that Daenerys meets during her travels. This healer has unique knowledge of magic that could help Daenerys in her quest for the Iron Throne.
Another fanfiction concept could be a 'what if' scenario. What if Jon was the one who found Daenerys when she first landed in Westeros? This would put Jon in a position of power and knowledge about this new queen. He could act as her guide through the complex web of Westerosi politics. Their relationship might develop more organically as he helps her navigate the land he knows so well, and perhaps they would fall in love more gradually, away from the prying eyes of the other lords and ladies.
One interesting scenario could be Jorah saving Daenerys from a secret assassin in a crowded market. His loyalty and combat skills would shine through as he fends off the attacker.
One plot idea could be that Daenerys and Arya meet on the road. Arya, being the assassin she is, is initially suspicious of Daenerys. But as they start talking, they realize they both have a common goal of bringing justice to Westeros. Daenerys offers Arya a position in her court, which Arya hesitantly accepts. Together, they plan to take down the corrupt lords and make Westeros a better place.
One idea could be a fanfic that focuses on the backstory of a minor character, like Gendry. Explore his life before he met Arya, how he survived on his own in King's Landing, and his early days as an apprentice to the blacksmith. Another could be a story set in a different part of Westeros during the events of the main series, perhaps in Dorne, and show how the political unrest there affected the common people. A third idea would be to create a fanfic where the White Walkers are not the main villains, but instead there is a new, more insidious threat emerging from within the Seven Kingdoms itself.
One idea could be to write a fanfic about a character who was thought to be dead but actually survived and is secretly plotting revenge. For example, a Stark family member who everyone believed perished in the Red Wedding.
By giving him a unique power. For example, not just the ability to control dragons like his mother, but something more. Maybe he can communicate with animals in a way that no one else can. This would set him apart and make the fanfic more interesting.
One interesting fanfiction could be where Jon and Daenerys form an alliance much earlier and together they face the White Walkers. They combine their forces and knowledge, with Jon teaching Dany about the North and its ways, and Dany sharing her dragon - riding skills with Jon. This could lead to a more united front against the common enemy.
One idea could be exploring the breeding of dragons in a different way. Maybe a fanfic where characters try to breed dragons with unique traits by using magical or scientific means in the 'Game of Thrones' world. Another could be about the breeding of horses with special abilities for the knights to ride into battle. For example, horses that are faster or more resistant to the cold of the North.