At the intersection of crack and tragedy, I have this fic idea about Zuko getting time looped during the day of his Agni Kai.
The first few loops are painful and traumatic. (Well, they're all painful and traumatic, but after the first fifty times... even getting half your face burned off by your own father gets old.)
After a while, he manages to stay awake long enough to hear Iroh crying at his bedside, begging for Zuko to stay. Pleading with the spirits, please, not him too.
(And then it takes more time for him to realize who visits him after Iroh falls asleep. She doesn't say anything.)
Zuko makes a Plan.
In the mornings, he tracks down Iroh or any experienced firebender, and he learns. So what if he isn't good? He'll make up for it the same way he always does: with hard work. He has the time.
(One of these days, Uncle won't have to spend the evening crying to the spirits.)
He gets better. Far better than he has any right to be. Iroh is thrilled on the days when he manages to catch him and not one of the other masters. Every time, the other masters barely tolerate him until he shows them. Iroh is always patient and kind.
Middays are reserved for Azula. A sister is a sister, and maybe... maybe Azula just needed somebody after Mom left.
(Zuko got that wrong, too. He's pretty sure he died the first time, and this is the spirits punishing him for being a bad son, a bad brother, a bad prince. He'll get it right, eventually.)
And at sunset, he still tries to plead with his father. Ozai will never hear him, but he has to try.
(A few hundred burns to the face can make you hate a man.)
But no matter how hard he tries, he can't beat Ozai. His skills improve, but his body doesn't - it will always be thirteen, with undeveloped chi paths he can barely break through to, and Ozai is a man in his prime.
Until one day he fights so well that Ozai halts the battle. He has the old general (after all this time, Zuko has completely forgotten the general) brought up, and orders Zuko to give him a mark of shame. To prove himself a good son and a good prince.
He stands above the general and looks at his tears and his shaking hands and his panicked eyes and he understands.
This time, Zuko earns his scar with pride.
(And when Iroh cries at his bedside, he reaches out and squeezes his Uncle's hand: I'm here, I'm not leaving.)
(And later, when Azula comes in with her soft steps and doesn't say anything, Zuko cracks open his good eye and gives her a smile.)
(And when he and Iroh set out the next morning, it is with purpose.)
(They leave behind a princess who knows that her father is not invincible.)