Anon asked: Modern zucest au where Azula is a typical bratty annoying sister that drives Zuko nuts: she always invites her friends over and forces him to hang out with them and basically treats him like a bellboy, telling him to bring her and her friends various items. She messes things up and gets him in trouble, she basically owns his car: always driving and taking it to wherever she wants. Zuko just takes her shit patiently, until one day he gets too fed up and decides to teach her a lesson.
She'd enter his room without knocking and just grab something she wants, and Zuko would grab her arm, pull her back and tell her to ask to borrow it like a minimally civilized person. She'd laugh in his face, and he'd tell her she can't keep treating him like this, and that she better change or he'll teach her some manners. She laughs in his face again, Zuko snaps.
He'd slap her, then forcefully lay her across his lap, lift her skirt, and spank her hard, over and over, making her tear up. Zuko says he'll stop when she apologizes, but Azula still refuses to do so. He'd pull down her panties to hit her directly on her skin… and see that Azula is wet.
He'd get hard immediately, and would gently runs his fingers all over her wet pussy, teasing her making her squirm. The second he offers to give her a reward if she acts like a good girl, Azula apologizes. Since he is an honest guy and a good brother, Zuko gives her what she wants and fucks her all night.
Anon asked: Azula deliberately misbehaving (to a lesser extent now) in order to get her brother to punish and reward her (after she apologizes).
*pervy laugh*
I can see her also doing nice things for him when she wants to go straight to the reward. However, I don't think Zuko is always skipping the spanking on those cases. He likes seeing her ass turning red and Azula can't complain since it does turn her on.