He’s there when they’re brought in. Zuko. The useless son of the second prince. Warden of the biggest and worst prison in the fire nation. Where he is far away from the more important family members, so they wont have to look at him, and be reminded that their bloodline isn’t wholly pure.
The gaang wont know that until later of course. Right now, Zuko just seems like another insurmountable blocade in their quest, and it brings them that much lower, to know that he is here, and will be taking care of them personally.
Zuko makes sure to be there the moment they’re bought in. He has to see if it really is the avatar, and, more importantly, if the rumors are true. The rumors of him being a little boy, even younger than himself.
They all are, both the avatar and his two companinons. And oh, how it tears at him, so see them so broken. It is clear that their capturers have not been kind to them, and he feels even worse, knowing that he will have to continue the charade, even just for a little longer.
He has to get them securely behind the walls and bars of his prison, and his personnel, before he can talk to them properly. Before that, he will have to play the good, disgraced prince, looking for approval in a world where violence is the first and best answer to everything.
It starts like this.
Zuko is a gentle boy, loyal and obedient. He grows up in a household where violence and cruelty is the norm, but he never once speaks out about it. Until he does.
He is 15 years old, when his uncle and father finally decide to agree on something. Unfortunately, that something is sending his mother into exile, with a target on her back, and only the barest minimum of protection. She dies.
He doesn’t find out until later, that the target on her back is from a hit requested by his father, for the discovery of her unpure blood, but still, her exile is enough to get him to doubt his father and the firelord.
But questions of that kind are heavily frowned upon, especially in the royal family, and so he is reprimanded harshly, any time he dares ask them.
He stops almost immediately of course, but his transgessions are not easily forgotten, and by the time he turns 16, and is recognized as a fully adult member of the family, ready to receive his agni-granted post by the firelord, he is sent to the lowest post a royal-blodded can be allowed to take, without the rest of the family losing face.
And then comes the rebellion.
It is nothing grand, nothing even truly visible.
The others of his family think him a weak firebender, and a weak mind, too soft for their preferences.
He is not. Not truly. He is the leader.
The leader of prison, true, but also the leader of all the people he can gather under himself, and his banner, who, like him, think that the firelord and his family is too cruel and violent not to be brought down.
It is hard, of course. Especially at the start, since he is still a member of the aforementioned family, but by the time the avatar awakens in the south, and one of the more prestigeous heirs, his sister Azula, is sent out for him, Zuko has his entire prison staffed with only his supporters, and is slowly but surely reaching out to the other nations.
This is just the start, but other plot-points include;
Iroh being the actual firelord, because he didn’t lose his son in the seige of ba sing se.
Iroh’s son being a dick, like the rest of his family.
Zuko being very mature, but also caring.
Zuko not actually demanding the Avatars help, like most others, but wanting the avatar trained, and fully prepared, and f*ck the consequences, 'cause a mentally instable, not very well trained avatar, is most likely more dangerous than another emergence of sozins comet.
The Gaang being totally and utterly flummoxed by zuko, because …What…. What the f*ck…. The prince…PRINCE is the leader of the huge resistance movement….????? And he doen’t want to kill us?… Or lock us up…? Or even really want us to help him, cause he’s got everything under control, like the royally raised prince he is???????
Potential for eventual zuko/sokka, but not necessarily