"I have a vision of the future, Roku."
With that Sozin climbed onto his Dragon. Roku watched in disbelief as the best friend he had ever had flew away, leaving him to die. He wished Sozin had never come to help him at all. To give him hope, to go out of his way to help him fight the volcanoes, only to abandon him was the cruellest thing the Fire Lord could have done to the Avatar.
Roku choked on the smoke, filled with terror, rage and despair. He knew Sozin was obsessed with expanding the Fire Nation but it had never even crossed his mind that the man whom he thought of as a brother would actually let him die in order to do so. Roku wished he had killed Sozin when he had the chance.
As the lava descended, Roku heard a familiar roar. The smoke made it hard to see but with the last of his strength, the doomed Avatar managed to look up to see his Dragon, Fang, hovering above him. He hadn't even realized Fang was still there, too preoccupied with fighting the volcanoes. He had told the Dragon to leave but part of him was hoping that Fang would disobey him. He knew it was selfish but he really didn't want to die alone. He was scared. He no longer felt like the Avatar but a feeble old man.
Would Fang abandon him like Sozin had?
Fang sensed his masters despair. He was tempted to go after Sozin and tear him apart but he couldn't leave Roku. He was better than Sozin. At the very least, perhaps Fang could comfort Roku and make the pain of Sozin's betrayal more bearable.
Fang flew down and coiled around his beloved master, knowing that neither of them would survive this. Even a Dragon couldn't survive in lava. Fang looked at Roku and the elderly Avatar's fear, anger and pain was quickly replaced with love and gratitude. There was no fear in the Dragon's eyes, just warm love and a strong resolve to stay by his side until the very end. Roku didn't have time to thank Fang for staying but he was grateful beyond words. Roku put his hand on Fang's scales, feeling their warm and comforting roughness as the lava washed over them. In their final moment, the Avatar and his Dragon took comfort in each others presence.
Sozin had never been Roku's best friend.