I always thought it was extremely powerful that ATLA decided to portray a younger female (Azula) abusing an older boy (Zuko) and not have it be played for laughs. It’s portrayed to be just as horrific as it would be if it were the other way around. And I loved how Zuko was never mocked for being frightened of and traumatized by his little sister. Because boys—just like girls—can be victims, and girls—just like boys—can be abusers, and I love how this show decided to show that
There is so much that is wonderful and almost unheard of in Azula’s storyline. She is as you say a younger girl abusing her older brother. We don’t see a lot of acknowledged sibling abuse, much less sibling abuse of an older brother by a younger sister. We also almost never see acknowledged abuse within a friend group. When we see abuse in fiction, it tends to look pretty much the same, a husband abusing a wife, a parent abusing their child. When we see do see other kinds of abuse, it’s almost never acknowleged as abuse, or as really harmful by the narrative. Azula is a complete departure from this. She, a fourteen year old girl, is always acknowledged by the narrative as a credible abuser, who is capable of real harm, and Zuko, Mai, and Ty Lee are never shown as weak or somehow at fault for being her victims. They are allowed to be scared of her, to be traumatized and hurt by her, and when they do get away from her, this is shown as an act that takes real strength and bravery.
Fiction is a mirror of real life and when you never see your own experiences reflected in that mirror, it’s difficult to name them and see them for what they are. I remember when I was in high school, I told one of my teachers that my relationship with my abuser was like an abusive marriage. At the time, she was still stalking me, and I had only just moved to a new state and my nerves were raw, and the fear I had lived with for four years was refusing to go away. But though I could say that my experience was like being in an abusive marriage even then, it took me several more years to be able to name what had happened to me as actual abuse, not just like abuse. And it took me even longer to stop feeling like a fake victim because my abuser was younger than I was and another girl. If I had seen Avatar: the Last Airbender earlier, that process might have been much easier.