One possible fanfiction could be about Joffrey's brother Tommen growing into a wise and just ruler. He could be shown learning from the mistakes of his older brother. He might start secretly training in combat and political strategy, with the help of some of the more noble characters in the series, like Tyrion perhaps. He could then start to make changes in King's Landing, trying to reverse the chaos that Joffrey had caused.
Well, clearly Joffrey is one of the main characters. His brother, depending on the specific fanfiction, could be any of the other male siblings in the story's universe. It could be a brother who is more kind - hearted and has to deal with Joffrey's difficult personality.
One interesting plot could be about the two brothers having to overcome family rivalries and court politics together. They might start off on bad terms but gradually come to understand and support each other.
The twin brother might befriend Tyrion. In the original story, Tyrion is constantly undermined by Joffrey. But the twin could see Tyrion's intelligence and value. Together, they could form a powerful alliance against Cersei and Joffrey. They could work towards a more just rule in King's Landing, reforming the laws and improving the lives of the common people. This would completely shift the power dynamics within the Lannister family and in King's Landing as a whole.
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.
Sansa Stark is frequently in these fanfictions. As someone who was a victim of Joffrey's cruelty, if he is in a time loop, Sansa might find herself in a different situation each time. Maybe in one loop Joffrey starts to treat her better, which would completely change her perspective and her own actions within the story. Also, Cersei Lannister could be involved. As Joffrey's mother, she would be very concerned about any changes in her son during the time loop and might try to interfere to keep things as she wants them.
Well, if it's about Myrcella, Joffrey's sister (but still in the family dynamic), she could be kidnapped not for political reasons as in the show but by a group who wants to use her to expose the incestuous nature of the Lannister family. She then has to decide whether to go along with it or try to protect her family's secrets while also trying to survive. This could create a really complex and morally ambiguous situation.
This book was called "Traveling with the LoL System". The characters in the book included: The male lead was Greencrith, the female lead was Margaret Tyrell, the male lead was James Lannister, the male lead was Tyrion Lannister, the male lead was Jon Snow, the male lead was Tywin Lannister, the male lead was Hound, the male lead was Tormond, the male lead was Robb Stark, the male lead was Joffrey Baratheon, the male lead was Varys, the male lead was Pettir Baelish, the female lead was Sansa Stark, the female lead was Cersei Lannister, the female lead was Daenerys Targaryen, and the female lead was Yggaret. Female supporting role-Missandet, female supporting role-Caitlyn Tully. This book can be read on Qidian Chinese website.
The Game of Thrones with a LoL System by 3NRGPG. It was a fantasy/sword and magic novel with a system style, LOL, hegemony, fantasy history, and dragon elements.
[User recommendation: After traversing the Game of Thrones.]
Winterfell's deviant ghost soldiers were approaching the city, and Mother Dragon was preparing to mount her dragon to fight. It was as if a bomber had flown past his head, and his eardrums were rumbling.
Looking up, a giant dragon swooped down on the Valkyrie. Drogon looked back at Mother Dragon (Why can't I do this? )
Following that, another giant dragon flew over the wall curtain, scattering rocks, piercing rocks, and piercing through rocks in one go. Veselion tilted his head and thought (Isn't the dragon only capable of breathing fire? )
Then, another giant dragon rubbed its spiral ball and spat out a life form disintegration ray. The Night King touched his scalp and felt a chill.
I hope you will like this book.
He could marry a foreign princess. This would bring a new dynamic as she might have different cultural values and beliefs, which would create interesting storylines as Jaime adjusts to being with her.
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.