There could be a really interesting fanfic where a Dragonborn enters the world of Game of Thrones during Joffrey's reign. Maybe the Dragonborn would initially be seen as a threat by Joffrey. But the Dragonborn's powers could change the power dynamics in King's Landing. For example, if the Dragonborn has the ability to control dragons, it would be a huge advantage over the Lannisters who rely mainly on their wealth and military might at that time.
In the context of the fanfic, the Dragonborn's presence could also expose Joffrey's weaknesses more clearly. The people of Westeros, seeing someone with such great power (the Dragonborn) who is not as cruel as Joffrey, might be more inspired to rise up against Joffrey. And Joffrey's own allies might start to question their loyalty to him when they see the Dragonborn as a potential new power player in the game of thrones.
There are some really interesting fanfics out there that combine the concepts of a Dragonborn in the Game of Thrones universe with Joffrey. One I've read had the Dragonborn as a sort of mysterious figure who arrives in King's Landing during Joffrey's reign. The Dragonborn's presence throws the power dynamics into chaos as they have their own set of powers and motives. It was really fascinating to see how the author played with the different personalities and politics of the Game of Thrones world in that fanfic.
Power is a very common theme. The Lannisters are known for their lust for power in the original series, and fanfictions often explore how they gain, maintain, or lose power. Family loyalty is another. Despite their many flaws, the Lannisters have a strong sense of family loyalty, and this is often a central theme in fanfictions.
In the Game of Thrones novels, Tyrion Lannister remains alive. His character undergoes many challenges and developments but doesn't meet his end. The author has kept him as an important part of the ongoing narrative.
Consider their upbringing. If they were raised away from the main Lannister stronghold, they might have a different set of values. Maybe they were raised by a kind - hearted servant who taught them to be more empathetic. So their personality could be a mix of Lannister pride and this new - found empathy. They could be conflicted between loyalty to their family and doing what is right according to their own conscience.
In the official 'Game of Thrones' series, it was Sansa's necklace (which was actually a poisoned device) that led to Joffrey's death, not Arya. However, in some fanfics, authors might create alternate storylines where Arya kills Joffrey. But these are non - canonical and just creative interpretations by fans.
Perhaps an OC Lannister who is a talented healer. In a world full of wars and battles in Game of Thrones, a healer Lannister could be an interesting addition. They might have to deal with the moral dilemma of healing both their own family's enemies and allies. They could also have a secret love affair with a member of another house, which would add a layer of drama.
There are no appropriate'sex stories' in a positive sense about Cersei Lannister. Her character is more about her ambition and her role in the power struggles of the Seven Kingdoms. Her relationships, like with Jaime which was incestuous, were part of her downfall and her complex character arc. It was a way to show the moral decay in the world of 'Game of Thrones' rather than just a titillating story.