A/N: Thank you, Boys like Girls. ;)
She didn't know why, but there was something about Zuko that soothed her mind infinitely, whether it be running her fingers through his always-soft, shaggy hair, or tracing the contour of veins and splaying her hands against his pallid marble skin, or (her favourite) breathing him in—the scent of incense and ashes and glowing embers with flickers of warmth plying her nostrils.
(Yes, all typical Fire Nation smells, Katara knows: the very essence of the bloodlust and violent destruction that had sprung from the heart of its Nation. But instead of scratching painfully at the back of her throat, Katara is surprised to find how easily she breathes it in, and how it smells homey, almost woody, tinged with nostalgia and comfort and something distinctly like chamomile. For some reason, it doesn't remind her of pain of destruction. It just glows, like fireflies or jewels or golden pastry puffs.)
So after almost getting knocked off the temple by one of Aang's stray runaway air scooters, receiving a bruise the size of a kimodo-rhino after Toph accidentally threw a boulder at her spine, then having their dinner blow up in her face after she had (unknowingly) put in one of The Duke and Teo's pepper bombs, you should know it was fairly obvious that Katara was having a Very Bad Day.
So I'm sure you'll agree that it was perfectly justified when after the end of her Very Bad Day, Katara stalked up to where Zuko had been meditating in front of the sunset, yanked him towards her without warning, then buried her face in his neck, her fingers cradling the side of his unscarred face and resting in a black patch of hair, breathing in his scent deeply and slowly.
And Zuko, smart boy that he was, had learned enough that when Katara did something like this, you let her do whatever she wanted first, then questioned why later (unless, of course, you wanted your— er…manhood frozen off.)
A minute passed. Zuko ventures a interruption. "Uh…Katara? What're you—"
"Shut up." Katara snaps back as she inhales another lungful of his smoky aroma. "I'm self-medicating." Her fingers slowly skim over a portion of his cheek. Zuko's heart skips a beat.
They stay like that for quite a while.