Set sometime in the future, after DOBS. No spoilers, just speculation.
The Apothecary's Tea Cup
Zuko is not a master of tea, not a connoisseur or a lifelong student. He does not have the palate for discerning between leaves that have been withered dry and leaves that have been rolled, or guessing where a stash was grown by the quality of its bitterness. He only knows that white tea is too plain for his Uncle, black tea is what his sailors would always drink, and--if absolutely forced into some kind of preference--all he personally wants in his boiling water are fresh lemon leaves and a bit of honey. So he is not the man to ask for flavors or advice, and he can't tell Katara what kind of tea will let the bloodied, battered Avatar sleep a little easier.
He approaches them warily, observing the too-quiet scene of Katara leaning over a normally vivacious boy, the former silenced with concentration and the latter silenced by something far worse.
"They're not going to kill the pain, but I did find mint leaves in the ravine. We can brew them, and if you have the last of the honey it will go down easier. He's lost a lot of water with the sweat and vomit, and if he doesn't drink something soon he might go into shock."
"I have the honey, in my bag. Will it mask the taste of echina root?""He won't thank us for ruined teeth in his later life, but if you use enough, yes."
She accepts the tiny bundle into her palm, laying the cloth open like petals of a delicate flower. In the center there are mint leaves instead of stamen, and she carefully drops several large pinches of the fresh greens into a boiling pot. Katara then re-wraps the remaining mint and tucked the package into her belt, raises her eyes to the prince, and says, "We've done all we can do, Zuko. We've healed him and we're giving him something to fight infection, now we just have to wait now for his body to catch up."
The prince paces. "I can't just stand here. I need to do more. I can't wait and do nothing when I know that he's almost dead, again, because of me."
"This isn't about you," Katara tells him, but there's no reprimand in her, only gentleness. Zuko knows without looking that she is crying, a tear drifting down each cheek, because the hitch of her breath gives away what even her voice does not. "Sit with us. Haru has the watch."
Zuko nods at last. He folds his legs and places his elbows on his knees, hands clenched and unclenched. As he watches Katara bends a strand of the mint-echina tea into the mouth of the young boy resting on a bed of leaves. When Aang swallows, throat bobbing delicately, the prince and the warrior feel the wires around their hearts loosen.