About Aang, and feeling very left out:
The world is singing, but he cannot sing with it. It tells him the war is over. It tells him certain countries are building themselves up again. They tell him there is a new Firelord, one who actually brings peace and goodwill. They tell him the 'bad' advisors are being fired, and the new ones actually care about people.
They tell him the world is growing, and it is peaceful, and he smiles, and looks for his voice. He wants to sing with them, to say that he is growing and peaceful too, but it's harder than it should be. After a while, he feels like a fool, always trying to open his mouth and sing, when he just… can't, so he stops.
There is a melody playing, but he will not join. He will not join the dances of the Water Tribe, and he will not eat the traditional foods of the Fire Nation. He will not understand the significance of the Earth Kingdom rituals that to him, frankly, make no sense. He will not ever be able to pick up his instrument and play along.
The world is singing, but it does not have room for him. He thinks it did, once, and he misses it. He remembers how he and his friends would sing and sing and sing, and the world would be filled with a melody of so many instruments it felt it would break. He remembers the ceremonies that he can't do now. He remembers the traditional food of the Fire Nation that somehow worked for everyone. That's gone now, and his voice has gone silent.
He wonders if the world is missing something, to have him gone. He supposes if it was missing something, it would ask him to join in song. He would, really, he would. He'd love to join - to sing, and to play, and to make music. But the world doesn't want him. So he sits and thinks about how the world doesn't want him to join.
Yet, that's too much of an accusation, isn't it? Because it's not the world that doesn't want him to sing - at least not all the time. Yes, there are times when he's hesitantly asked to leave the table because it's an Earth Kingdom only event, but most of the time, he can tell when he's supposed to leave, and does it by himself.
He's gotten good at that, now, at seeing when he's not wanted at the table, or the festivity, or when it's just really a family thing. He knows they're not trying to hurt him, but they deserve to be with their families. Maybe he does, too, but he knows that's not an option, and doesn't want to even think about asking for it.
And so, he doesn't sing. He doesn't sing, even as the world holds the loudest celebration and song it ever has. He doesn't pick up his dusty instrument, even as the symphony increases in timbre and quality for the first time in the war. He just… listens.
Maybe, he does feel a little left out, but what's he supposed to do? His voice, which doesn't want to sing, and his instrument, which doesn't want to play, simply don't fit in with the rest of the song. They haven't, actually for 100 years. He doesn't think they ever truly will again. But… that's okay. It's a pretty song. He can listen.