If Arya kills Joffrey, it could also lead to a change in the balance of power among the noble houses. Some houses might see Arya as a hero for getting rid of the cruel Joffrey, while others would condemn her as a murderer. This could lead to new alliances forming and old ones breaking. The Night's Watch might be affected too, as the political turmoil in the south could mean less support or resources for them, and more focus on internal power struggles in the Seven Kingdoms.
There would be chaos. Joffrey is a king, so his death would create a power vacuum. His mother Cersei would be furious and would likely start a manhunt for Arya. The Lannisters might declare war on Arya's family or allies. The political landscape would be completely disrupted as different factions would try to take advantage of the situation.
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.
In the fanfic, Arya might kill Joffrey during a big event. She could blend in with the chaos. Since she has great agility and combat skills, she could quickly approach Joffrey while everyone is distracted. For example, during a tournament or a grand feast. She could jump from a balcony or some hidden place, stab him swiftly, and then disappear into the crowd before anyone realizes what has happened.
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.
If Arya killed Joffrey in a fanfic, one possibility is that she would become an instant target for the Lannisters. They would stop at nothing to avenge Joffrey's death. Arya would have to go into deeper hiding or rely on her Faceless Men training even more. Maybe she'd have to flee across the Narrow Sea and start a new life in Essos, constantly looking over her shoulder for Lannister assassins.
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.
The Stark family would be in a much stronger position. Robb Stark would not be killed, which means the North would remain united under his leadership. This could potentially change the entire power dynamic in Westeros. The Boltons and Freys would be seen as traitors and might face severe consequences from the other houses.
One idea could be a story where Arya meets Lemon in a tavern during her travels. Maybe Lemon has some interesting information about Arya's enemies, and they form an unlikely alliance to take on a common foe.
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 fanfic, Arya's warging can be a really cool concept. Some fanfics might show her warging into animals to gain information or use their skills for survival. For example, she could warg into a wolf like her siblings and use its enhanced senses to track down enemies in the chaotic world of Westeros.