It was mentioned in a short comics Piandao was the one who tought Zuko how to use the dao swords, and it's bothered me they didn't talk in the episode they met the masters.
English isn't my native language, so forgive me for any minor mistakes.
Disclaimer: The Avatar universe belongs to Michael Dante DiMartino and Bryan Konietzko and Nickelodeon. I don't own anything.
After the eclipse Zuko realized where is uncle went. After their encounter in the desert Iroh explained to him about the Order of the White Lotus. Zuko knew he had allies from all around the world and he probably reach out to him and he is going to be alright. Iroh also told him his old master, Piandao is part of the order as well so he knew he could reach him if he needs to find is uncle. But using June was faster, and it was urgent. But maybe it was too fast because he wasn't sure how to start the conversation with his uncle.
Zuko knew it was time to face his uncle, he was glad at the opportunity to meet him before they charge back to the war not knowing if they are going to return alive. If his uncle will go fight his fath- no it's Ozai not his father, Iroh was always more father to him then Ozai. But if they are going to fight only one of them will be alive in the end and he didn't know which one of them will survive this battle. He wasn't sure how easily he even agreed to volunteer his uncle to fight Ozai, but Aang disappeared and he didn't saw any other option to win this war besides asking his uncle to fight Ozai. But how he could ask his uncle to go and fight Ozai after what he did to him? He probably hates him and he has a good reason for it. He doesn't deserve his uncle forgiveness.
"Where, where is he?" Zuko asked, looking around at the tents, you can hear in his voice that he is nervous.
"Your uncle is there, prince Zuko." Piandao pointed at the biggest tent in the camp.
Zuko stared at the tent for a moment and then he looked at his old master starting to walk away. "Wait, master..." he stopped him.
"Yes, prince Zuko?" Piandao turned to him and looked at him.
"Does he..." Zuko wasn't sure how to ask it. Piandao was his old master and he was a close friend with his uncle. It was his uncle's idea for him to train with Piandao because he was a bad firebender. He hurt his uncle but now under the fierce gaze of his old master he can't help the feeling he also let down Piandao as well. Zuko lowered his head, couldn't even look him in the eyes. He did so many mistakes, he doesn't deserve their kindness. Piandao and Iroh were always nice to him and were like father figures to him and he just ignore that and was ungrateful and selfish. He let his desire for acceptance from his father to blind him from his values and beliefs.
"Zuko?" Piandao called softly, snapping his former student from his thoughts.
"Sorry master. You think... does he even wants to see me?" He finally asked, still staring deep to the ground below them. In that moment he wished he could have been an earthbender so he could bend the ground to swallow him.
"Yes, he was really sad about everything that happened. He misses you." Piandao assured him.
"Doesn't he hate me? He has every reason to hate me. I betrayed him." Zuko said with sadness in his voice.
"Prince Zuko, I can assure you he is still loves you. Your uncle misses you dearly and he always believed in you, even after what had occurred in Ba Sing Se. It's going to be alright." Piandao told him and guided him to the entrance of the tent.
"Aren't you disappointed from me?" Zuko decided to ask. He might not hurt directly his old master like he did to his uncle but Piandao was a man of honor and honest reputation and Zuko is not answering his values anymore.
"No, I'm proud of you. You are here to amend your relationship and apologise and that's the important thing." Piandao promised him with a wide smile.
Zuko nodded at him and sat there for a moment to gather his thoughts. Piandao saw Sokka's sister approached to their directions so he decided to let Zuko's friend help him as well before he is going to talk to his uncle.
Zuko was needed a moment to breath and think before their departure to the Fire Nation. He knew he has to fight Azula and they are going to defeat his father but he didn't think about who will take Ozai's place after he's gone. He knew he was the crown prince but with his banishment and then his betrayal he didn't feel like he has the right to take the throne. When he was eleven and he became the crown prince being fire lord felt very far and when he was banished, he didn't let himself think how it would be when he'll be the fire lord. But now he needs to take the crown. His uncle doesn't want it and he wasn't sure if he is ready to claim it.
Suddenly Zuko felt a pain forehead. He groaned while rubbing it and looked to see what he hit. It was a Eel hound. Piandao was busy preparing it for Sokka's travel. He walked right into the area the animals were held in an improvised stalls with ground blocks that Bumi probably bend so they will be used as fences.
"Prince Zuko, are you alright?" Piandao's voice snapped him from his thoughts.
"Yes, it's just a small bump, nothing else." Zuko promised him.
"What's on your mind? It's not like you to lose your focus like that." Piandao asked softly.
"It's just that I don't think I'm ready." Zuko admitted.
"To fight your sister?" Piandao wondered, "I know it can't be easy to fight with a family member but you learned a lot from your last time," he assured him.
"To take the crown. I made so many mistakes. I'm not deserving it." Zuko said.
"You deserve it, being the fire lord is your right place. You are here to atone your mistakes, you learn from them, that's the important thing for someone who suppose to lead their people. You are going to be a great fire lord and it would be my honor to serve you." Piandao told him.
"It's still should be my uncle, my father stole the crown from him, he was the heir." Zuko said.
"When your uncle decided to join the Order of the White Lotus, we were really glad, he was royalty and we finally could believe we can end the war because he could take the throne and stop it." Piandao mentioned.
"Exactly, he deserves the crown, he'll be a great fire lord." Zuko repeated.
"And so do you. I don't think he should be the fire lord now, I realized you are better suited for this task now." his master told him.
"Why? He leads the Order of the White Lotus, he is the one who represent harmony and peace between the nations, he is the best man for the job." Zuko said.
"No, he is not. You are the best. I know it's scary for you to take the crown but it's your destiny. Your uncle is a symbol for the past, I realized it now, you are the future. Iroh is a general, he almost breached into Ba Sing Se. Yes, he is here to free it, but he still a symbol for the war. You joined the avatar to stop the war, you are a symbol of the peace. You returned to the royal palace and you received back everything you wanted and you sacrificed everything to join the avatar. You chose peace and harmony over everything else to stop the war, so you should continue the path to balance the world." Piandao told him putting his hands on the boy's shoulder.
"You really think I can do that?" Zuko asked silently.
"Yes, and you going to be the best fire lord the fire nation had in centuries." Piandao assured him.
"Thanks, master." Zuko bowed to him and hugged him.