He was standing in a dark void with someone calling his name, someone strangely familiar. Am I in another fever dream? he thought, though he hadn't felt at all sick when he'd gone to bed. His next guess would be the Spirit World, but only few people could visit there and under certain conditions. Zuko turned to see the ghostly figure of Fire Lord Sozin beside him, and his eyes widened.
"What's going on?"
"Come with me, Fire Lord Zuko," Sozin said, "for there is something you need to see. I warn you, though, it will be very upsetting."
Zuko sighed.
"No thanks, I know what you did and why everyone worshipped you for so long. I've found my own way now, and-"
"That's why you need to see this," Sozin interrupted. "Do not worry. I don't intend to harm you or make you question your choices." Before Zuko could speak another word, they were leaving the void and stepping into the light. Zuko immediately recognized the scene before them as the Southern Air Temple.
"This is where Aang grew up," Zuko whispered. "But why-"
"Watch, Zuko." And suddenly the carefree scene before him changed to an image of Sozin himself betraying Roku, commanding many war ships and then back to the Southern Air Temple where benders and soldiers alike fought for their lives until the smoke cleared and all that remained of the Air Nomads were their bodies. Zuko shuddered, digging his nails into his palm.
"I've heard this story a million times," he choked.
"But not this part." The scene flashed forward to a century later, a frail skeleton, and-
Aang. Zuko felt his heart drop into his stomach. He was seeing the happy flashbacks of Aang's childhood years, the stories Aang had told him mixed with memories of himself going to the ends of the world to capture the Airbender, then finally fading back to Aang sobbing over his mentor's corpse and the realization that his people were gone, he was alone. When the scene faded away, Zuko realized he himself was crying.
"Sozin," he spat, "why did you show me all this? Don't you think I know what a jerk I was and how Aang suffered? Did you want to make sure I spent the rest of my life regretting it now that you could see I was learning to let go of my guilt?"
"Silence!" Sozin gripped his descendent by his shoulders, looking into his eyes. "I brought you here because in the last moments of my life, my biggest regret was betraying Roku and starting this war. And now that you've helped to correct my mistake, I wanted you to see my regrets."
"Why?" Zuko sobbed.
"Because Roku was my soul mate, just like Avatar Aang is yours," Sozin said. "And I couldn't rest well until I knew for sure that you wouldn't make the same mistake I did." He reached out to wipe away his great-grandson's tears. "And given your reaction, I can tell you won't."
"Never," Zuko said, sniffling. "Aang is one of four people who mean more to me than the world, and I'd sooner end myself than betray him."
Sozin nodded.
"Good. Now I can finally rest." The ghostly image faded along with the void, and Zuko woke up. The sun was rising and even as he wiped away his remaining tears, he knew it was going to be a beautiful day.