Well, if Aang joins the Fire Nation in fanfiction, it could lead to a total change in the power dynamics. He might try to reform the Fire Nation from within, using his Avatar powers for good in a different way. Maybe he'd start teaching the Fire Nation people about the other nations and promote peace and understanding among them.
The story would likely take a very different turn. Aang joining the Fire Nation could start with him being a sort of undercover agent, trying to figure out the secrets of the Fire Nation while pretending to be on their side. This could lead to some intense spy - like situations.
Aang might go into a deep state of depression. He has always been an emotional character, and having his heart broken by Katara, someone he loves deeply, could send him into a downward spiral. He might isolate himself from his friends and stop practicing his bending for a while.
One unique feature is the blend of two distinct universes. The Naruto universe with its ninjas and chakra system, and the Fire Nation from Avatar with its firebending and hierarchical society. For example, in some fanfictions, Naruto might learn firebending techniques, which is a cool crossover concept.
Katara could be heartbroken. She might initially be in denial, not believing that Aang has actually left. Then she could become angry, feeling betrayed by Aang's sudden departure.
Eventually, the class might come to understand Marinette's decision. As they struggle to do things on their own, they realize how much effort Marinette had been putting in. This could lead to them changing their ways and maybe even trying to make it up to Marinette if she decides to start helping again.
If Naruto joins the Fire Nation in fanfiction, he might bring new skills and ideas. His unique jutsu could be integrated into the Fire Nation's military strategies. Also, his never - give - up attitude could inspire the Fire Nation soldiers, leading to a more united and powerful military force.
Yes, there are many. You can start by looking on popular fanfiction websites like Archive of Our Own. Just search for 'fire nation loves zuko' and you'll find a variety of stories with different plotlines, from the Fire Nation's perspective adoring Zuko.
One possibility could be that she is sent as an emissary of peace. In the fanfic, she might try to use her waterbending skills to gain the respect of the Fire Nation people. She could start by showing them how water can heal, which is a concept very different from their own fire - based culture.
The Fire Nation, which has now become more of an ally, would also see this as a positive thing. Zuko, being Aang's friend, would be happy for them. He would see it as a sign of peace and unity among the different nations. The Fire Nation people might send some precious gifts as a sign of their respect for the union, as they know how important the Avatar and Katara are to the new world order.