DISCLAIMER: Nope i don't own any of the characters
I'm really surprised that no one has done this sort of thing yet. It seemed really obvious to me, oh well. ENJOY!
Zuko cast a glance at Aang and his eyes narrowed as a sudden thought came unbidden to him. Even among his once enemies, even without his uncle, he was with his family. The irony. But wait! Did the avatar know? Most likely not. Zuko grinned. It was time to have some fun.
"Is it true? That the Avatar is simply reborn and can call on past memories and lives?" Everyone looked up at their newest dinner guest. It was the first time he spoke to them after offering to teach Aang how to fire bend. They were a little shocked to say the least.
"Uh, well yeah kinda." Aang scratched the back of his head nervously. He didn't really know where Zuko was going with all of this and it slightly frightened him. The others apparently didn't trust him either. They didn't do a good job of hiding their suspicious glares though.
"Avatar Roku was the Avatar before you. Do you remember anything from his life?" Ah, so that was where this was all coming from. Zuko just wanted to know more about the fire bending Avatar. Well, that was an easy topic for Aang.
"Yeah! He showed me all sorts of stuff about his life!" Zuko glanced up from his bowl and looked Aang in the eye.
"Did he now? Did he show you his child? Or his grandchild?" Aang was now thourly confused. Roku had a kid? He didn't remember that part.
"So if Roku was reincarnated, that would mean that you, Aang, are Roku?" Zuko said this with a drawl that had Aang on high alert. His position also bothered Aang. He recognized the position that Zuko was in. If Zuko wanted to attack or be on his feet it would be in a matter of seconds.
"I suppose. What! HEY! LET GO!" Aang was wrong in his calculations. It didn't even take a second for Zuko to reach him. But this was an attack that Aang had never witnessed or even heard of before. He didn't know how to counter-attack. A quick glance told him that the others were not going to be of any use. They were staring at the two of them with looks of confusion and disbelief on their faces. All save for Toph who had a seemingly smug smile on her face. That scared Aang even more than Zuko's strange behavior.
"Zuko what are you doing?" Aang pulled away from Zuko and threw a glare at the Fire Nation Prince. It was quickly replaced by a look of horror at the wide grin across Zuko's face.
"Nice to finally meet you Grandpa."
Sokka would latter accuse Zuko of trying to give Aang heart failure, Katara would scold him about being more tactful and Toph would hand over her bet money and tell Zuko that she truly thought Aang would have handled the truth a little better than fainting. Aang would latter tell Zuko that if he ever called him that again then he would personally give Zuko a one way ticket to the Spirit World. Zuko was just glad that he finally found his sense of humor.
A/N: So Zuko's great-grandpa is Roku and Aang is Roku's reincarnation. Therefore Aang is Zuko's grandpa! Everyone has had to think this at one point or another. The idea of Zuko hugging Aang and calling him Grandpa was just too good to pass up. Have you hugged your Avatar today?