Anon asked: How do you think Azula & Zuko's "relationship" escalated throughout the years? Ex: hugs to kiss to grinding to handjob etc...
If they're left alone for just enough time, these two are likely to get a little too handsy with each other. They might "not like each other" very much (bullshit) but they're still socially inept, chaotic, curious children, and being siblings means that, whether they like it or not, there are somethings that only they can understand about each other and their lives since they were raised together AND are so close in age. They can't help but be naturally drawn to each other, and considering how intense and starved for affection these two are, it quickly grows into an obsession. As they grow up they might understand that what they do is "wrong", but it's the closest they can get to a regular sibling bonding, and they don't want it to stop OR to have any kind of "competition" for their sibling's attention (as if anything could ever come close to what they have anyway).
It'd start with attentive eyes and insistent glances making them notice every little thing about their sibling. Little quirks when they're nervous likes biting their lip, fidgeting, bouncing their leg, hands that toy with anything that's within reach. Memorizing every detail of their features, all of their scratches, bruises, birthmarks, and realizing that their sibling could be considered good looking - by other people, of course. Paying attention to their habits, which hair-style they prefer, which moves they usually go to when practicing their bending, what type of clothes they seem to like more and that make them look better. Noticing they got taller, that their body seems to be changing and that soon it will look nothing like the fading mental image they have of the times when they used to bathe together when they were even younger...
It'd lead to either spying to see each other undress or the classic "I'll show you mine if you show me yours", but either way getting answers will only make them more curious and wonder what it'd be like to touch each other. They wouldn't do it... at first. There would be many hugs that last a little too long, kisses on the forehead and cheeks, brushing each other's hair, tickling and sharing a few chaste, almost innocent kisses on the lips "just to know how it feels like" before they get to actually letting their hands gently roam their sibling's body. After that, bathing together and massaging each other becomes part of their routine.
Once again, that wouldn't be enough, and they'd just get curious about something else, especially as their hormones kick in as they get closer to their teens. Their bodies are changing even more, their reactions to their "experimentations" are getting more intense, and said "experimentations" are getting less and less innocent very fast. What was once just childish curiosity and a game, feels dirty and, like I said before, they both are now aware this isn't appropriate, but they don't care.
They've touched each other pretty much everywhere by that point. Their kisses are long, wet and sloppy now, and they quickly figure out that they both enjoy it when their sibling kisses and sucks on their neck. It leads to Zuko curiously licking and sucking on his sister nipples since she likes it when he teases them. Since he has also figured out that she likes it when he rubs her little clit and when he pushes his fingers inside her, he tries kissing her there as well. And Azula, who obviously knows just how to tease him to get him hard and how to stroke his cock to either get him off fast or to deny him release and see him squirm, tries doing the same, kissing his member and eventually taking it into her mouth. Their "hugs" are also pretty indecent now, with Azula sitting on his lap, rubbing up against his hard cock as they kiss. Sometimes they're fully clothed, other times they're wearing nothing but their underwear or bathing suits - if that.
It's all very awkward at first, but they quickly learn when to be gentle, forceful, fast, slow... and it just keeps on getting better. Eventually their curiosity gets the best of them once again, and Zuko gently, carefully enters her. On top of feeling strange for both of them, Azula also feels a bit of pain. But it's still too good for either of them to even consider stopping, and it quickly becomes another part of their relationship, as natural to them as their constant bickering and fighting, and as much of a secret as everything else they've done to each other.