An OC could be a foreign noble sent to King's Landing as part of a diplomatic mission. This noble has heard of Joffrey's reputation and is determined to find a way to either reform him or, if that fails, to remove him from power without starting a full - scale war. The fanfiction could explore the cultural clashes and political intrigue that result from this situation.
One idea could be an OC who is a healer in King's Landing during Joffrey's reign. The OC secretly tries to undermine Joffrey's cruel rule by using their medical knowledge to help those he persecutes. They might start by treating the families of those unjustly imprisoned. This could lead to a dangerous game of cat and mouse with Joffrey and his cronies as they suspect someone is working against them.
Perhaps an OC is a young squire who is assigned to Joffrey. The OC, seeing the true nature of Joffrey, decides to try and influence him for the better. He starts by introducing Joffrey to the stories of great and just kings from the past, hoping to inspire a change in his behavior. However, Joffrey's pride and cruelty often get in the way, leading to many tense moments between them.
Joffrey was a cruel character. It's hard to imagine a traditional love story for him. His nature was so malicious that any form of love seemed out of place. He was more interested in power and causing pain. So, in the context of the show, a real love story for him seems almost impossible.
One possibility could be that the oc, being the son of Drogo, has a claim to the Dothraki leadership. He could strive to unite the Dothraki clans in a different way than Daenerys did. Maybe he focuses on forging alliances with the other kingdoms based on mutual trade and protection rather than conquest.
One interesting scenario could be that it was actually a planned assassination by a secret alliance of the Starks and the Tyrells long before the wedding. They worked together in the shadows, using Sansa as an unwitting pawn. The Tyrells provided the poison, and the Starks had someone in place at the wedding to ensure Joffrey drank it.
Some fanfictions might focus on an alternate universe where Joffrey is not a king. He could be a simple knight, and the story could explore how his personality would develop without the power and privilege of the throne. He might learn humility and honor in a different way.
One interesting scenario could be a rewrite of their relationship where Joffrey is secretly influenced by a more benevolent force. This might lead him to treat Sansa with more kindness than in the original series. Maybe he starts to see the value in having an ally in Sansa rather than just using her as a pawn.
One possible plot could be that Joffrey's twin brother is the complete opposite in nature. While Joffrey is cruel and tyrannical, his twin is kind - hearted and wise. He could secretly try to undo the damage Joffrey does, like secretly helping the common people that Joffrey oppresses. He might also try to influence his mother, Cersei, to be more merciful, which would create a lot of internal family drama as Cersei is so protective of Joffrey.
The male OC Stark heir could be thrust into the role of leadership much earlier than expected due to unforeseen circumstances, like the sudden death of his father. He then has to deal with the challenges of ruling Winterfell, such as food shortages, disputes among the vassals, and the ever - present threat of the White Walkers. He uses his unique skills and the support of his loyal followers to overcome these obstacles and restore the Stark name to its former glory.
A fanfic involving a Dragonborn in the Game of Thrones universe with Joffrey could be a wild ride. Maybe the Dragonborn, with their dragon - riding abilities and magic, would pose a significant threat to Joffrey's tyrannical rule. They could swoop in on their dragon, causing chaos in King's Landing and challenging Joffrey's claim to the throne.
In some fanfiction, it might be Varys. He was known for his intelligence network and his ability to work from the shadows. He could have seen Joffrey as a threat to the stability of the Seven Kingdoms. So, he arranged for the young king's death, perhaps thinking that a more malleable ruler could take his place and be more easily influenced to make better decisions for the realm.
One idea could be an original character who is a bastard from a minor noble house in the North. They grow up with a unique skill, like being an expert tracker. They could get involved in the events related to the White Walkers early on, perhaps by accidentally stumbling upon one of their lairs. Their journey could then be about warning the other houses and trying to find a way to stop the threat before it reaches the major kingdoms.