Life without fire is a cold life indeed. What if Aang came to regret letting Ozai live?
He'd only been twelve. Twelve years old. Not even old enough to shave. Aang looks down at the former Firelord, strings of gray hair hanging limply over his once proud face, and wonders if there is any way to undo the mistake he'd made fifteen years ago.
Even now he could never kill someone in cold blood, but as Ozai lifts his head to meet the Avatar's eyes, Aang wishes he'd had the guts to do it in the heat of battle. They stare at each other for a long time, nothing needing to be said, except for the final words Ozai always speaks before Aang leaves:
"Kill me, Avatar. Finish what you started fifteen years ago."
At first Aang had responded with messages of peace, of mercy; protestations that he could never take a life. As he grew older and settled into life as the Avatar, his speeches turned into mere negations, a simple No, I can't, for the man who did nothing but roll his eyes at his childish philosophy.
After a while, though, Aang had stopped answering at all, and the eye roll had turned into a knowing smirk.
On the first anniversary of the battle he'd come to see the former Firelord for reasons he could not define even to himself. The next year he had returned for reasons just as opaque, and somehow it had turned into a yearly tradition. Every year since then had gone much the same: Ozai lifted his head and looked into his eyes, and Aang pretended to himself that he didn't see in them what he saw.
Chi bending. A lost art, reborn in the long-lost Avatar. An art he had taught only a select few, the most skilled benders and purest of heart.
An art he now taught no one.
Aang had done more that day than merely seal off Ozai's bending. He'd touched spirits with the man, seen into the deepest chamber of his heart, and Ozai had done the same. It wasn't really possible for two people to be more closely connected, and when Aang had finally realized that, it had made him shiver with a bone-deep cold. The look in Ozai's eyes told him that the man had always known.