For Aang, it was fate that had drawn him into the fires of war. The only accident of it was the time and place. It had been his duty to return the world to a state of peace, and somehow he'd managed it. But the more time that passed, the more incredible it had seemed that he'd managed at all. He'd been so young – a child traveling with others who weren't much older. He'd been strong, of course, with power and potential worthy of the Avatar, but that hadn't made him an adult. He'd had no choice but to grow up quickly in the face of all that had lay ahead – he and everyone else.
It was a miracle, really, that he'd awakened where he had. He could easily have ended up somewhere else, forced to start his journey with others who weren't as friendly. He could have ended up on the enemy's doorstep and been killed before he'd had the chance to fight back. Instead he'd met Katara and Sokka, and pulled them into the warzone along with him, ready or not. Although really, the truth was that the approaching flames had reached them long before he'd come along. He'd simply given them a chance to fight back. They'd stuck together, through joy and sorrow, and he couldn't have asked for better friends.
For Katara, it was a chance to make things right. With Aang's arrival came hope – a chance to quell the oppressive blaze that had taken so much from her. He could never have imagined how strong she would become, in every possible way. Her kindness became deep compassion, her passion became righteous fury and a thirst for justice. He loved her deeply, but more than that, he trusted her completely, and he was honored to have played a part in who she had grown to be.
For Sokka, it had been a chance to prove himself. He'd resented being unable to run headlong into the flames and fight for what was precious to him. But as the journey went on, it became clear that there was more to being a warrior than fighting one's enemies. He found his own kind of strength, and learned more about the world and its people than he ever would have on his own. Aang had come to see him as something of an older brother, long before his marriage to Katara had made it official, and he couldn't think of anyone else who fit the role better.
They'd met others, of course, and their group had continued to grow until the journey was over. Toph wasn't always easy to get along with, but she had her own sort of wisdom, and she took great joy in the freedom that their travels had granted her. And Zuko…he'd walked further through the flames of war than anyone else, and he had the scars to prove it. He'd been a fearsome enemy, once, but when he'd finally chosen a side, he'd become an even more valuable ally. Aang would never have thought they'd end up as friends, but fate could be funny that way. He liked this outcome a lot better.
Together, the Avatar and his companions had walked through the inferno and emerged not only alive, but victorious. He still wasn't quite sure how they'd done it, but things weren't over just because they had. He would dedicate the rest of his life to building a peaceful world out of the ashes that remained, and he prayed it would last a hundred years more.