Anon asked: What if Zuko and Azula were twins?
Zuko would 100% say that, since he was born first, he is technically the older sibling. Azula insists it doesn't count.
Their friendship during their childhood would be even more intense... but so would be their rivalry later on because people (Ozai) would be constantly comparing them, making Zuko feel insecure and resentful since he's not a prodigy like his sister.
They'd probably see themselves as two halves of the same person (and when she's feeling bitchy, Azula would say all the good traits of the person they are were in her half while Zuko got just the flaws). Add in the elitism of the Fire Nation and of royalty in general, these two are very likely to believe that the only person who has "the right"/is capable of taking their life would be their twin, since everyone else beneath them.
Once they learn that, in some cultures, it is believed that fraternal twins are a blessing from the Gods but that identical twins are a bad omen and that one or both of the kids must be sacrificed, there is a weird, tense silence between, since they both know that situation is much similar to the second case despite them being fraternal twins. Zuko is sure that if they had been identical, he would be the one to be sacrificed while Azula would be spared.
However, once they find out that in some parts of the world, it is common for twins of the opposite sex to be engaged since birth and that some legends say that lovers are sometimes reborn as siblings (mostly twins), they both blush and try to change to subject or leave the room, because they don't want to admit that the thought makes far too much sense for their liking.
After they do get together (because of course they will, it's just a matter of time) it would just feel so completely right that they would wonder how the hell could anyone (including themselves) have ever thought they could ever be with anyone else when they clearly belong together.