Anon asked: Age gap zucest headcanons? How would it have been different if Zuko was at least 8 years older than Azula?
A few months after Azula is born, Lu Ten dies, and Ozai would try and do the whole thing of "MAKE ME THE FIRE LORD, I GOT TWO DUMB KIDS WHILE IROH HAS NONE", which would lead to the whole "Kill your first-born thing". Since Azula would literally be a baby in this timeline, Ursa would, somehow, find out about it herself, kill Azulon and be banished.
With their mother gone, Iroh traveling the world, and Ozai becoming more and more of a monster with each passing day, Zuko would feel it was his obligation to help raise and protect his baby sister. Since he'd be the only person showing her genuine love as grew up, Azula would idolize him, and develop a crush on him (which Zuko would be oblivious to)
Since their age gap would be bigger, it would take longer for Ozai to realize that Azula could be more "useful" than Zuko, which would (for the most part) spare them of having a rivalry forced on them. Once did notice Azula's potential, Zuko would be very hurt to see that he is not so slowly being out-shined by the younger sister he helped raise and would start resenting both her and Ozai. However, once he's banished (he'd be around 16/17, while Azula would be around 8/9) and Azula is heart-broken to see him being forced to leave, he feels terrible for blaming her for Ozai's unfairness.
Ten years later, when Azula is the same age Zuko was when he was banished, Ozai sends her on a mission to bring him home as a prisoner. Since she loved her brother and never forgave her father for taking away the one person in her life that truly cared about her, she'd tell Zuko the truth once she found him, and try to find a way to either make Ozai forgive him… or to dethrone their father and let Zuko be the Fire Lord.
Zuko would be shocked to see just how much his sister changed and how much she has grown… and be horrified to realize he is attracted to her, not only because they're related but because part of him still thinks of her as a helpless little kid that needed to be protected from the world around her. Azula would instantly know what was going on (because let's be real, Zuko ain't subtle, specially not when he is nervous) and she'd be unbelievably happy - she had loved him since she was a little girl after all, and she had never thought there'd come a day where her Zuzu would feel the same.