A/N: This is my very first fanfiction story, so please go easy. Anyway, here's the full summary:
Just one thing, the summary below is for the entire series that i hope to write. it'll be about four installments, and this is the first. Hence the title, "Book One: Sound" the storyline for this particular story will be a little bit different, but the storyline as a whole idea, is that paragraph down there.

A new world is introduced to the Gaang. A world where people bend elements such as sound, electricity, steel, and plasma. The Gaang discovers that this new world is run by computers, and technology. Even more important, they discover that the leader of this world is much like the Avatar; the Ratava. The Ratava is the opposite of the Avatar, they bend sound, electricity, steel, and plasma. Aang discovers that this 'Ratava' is his sibling, and that they were separated back when Aang was born into his very first incarnation, a milliion years ago. Aang is forced to fight his own family and save the Avatar world, but after meeting with his long lost brother, he has second thoughts.

DISCLAIMER: I do not own Avatar: The Last Airbender. I also do not own Aang, Katara, Sokka, Toph, or any of the characters in the animated series.

BOOK ONE: SOUND

CHAPTER ONE: SECRETS

Years have passed since the fall of Firelord Ozai, and the Avatar world has been nothing but peaceful, until now.

XXX

Katara, Toph, and Sokka and I were walking peacefully in the prestigious and impenetrable city of Ba Sing Se. As we walked around the plaza, a poor old senior walked up to us.

"The-they're coming… the-the-the soundbenders!" the old man screamed in front of us.

I gave him a confused and annoyed look. Suddenly, a loud ruckus emitted from the end of the street. It was the Dai Li.

The old man ran swiftly into an alleyway nearby. As he ran by, he directed our attention to a poster on the wall. It was a picture of him with Chinese characters below. It was a mug shot.

"What is it?" Toph asked.

"Crazy old man, preaching crazy ideas. If found, please call the Dai Li." Katara translated.

"It's that creepy old guy, isn't it?" Toph asked.

"Yes." I replied. "They found him."

Sokka was about to rat on the old guy, by telling the Dai Li where he was, until Katara covered his mouth, silencing him.

"What was that for?" he scolded.

"Shush," she replied, letting the Dai Li pass by.

Once the streets were quiet again, Katara led us to the alleyway. As we looked down the alley, we saw a shadow.

"I want to know what he was talking about." Katara said. "If he really talking nonsense, then we'll turn him in."

Sokka ran down the alley, and we followed. The old man was crouching down in a corner, beside some garbage bags. As we stood around him, he looked up at us.

"You…what do want?" he asked.

"Finish what you were saying earlier." Katara demanded.

The old man pulled out some more full bags of garbage. I'm guessing it was his way of being welcoming. I like to think of them as beanbag chairs.

We sat down around him in a circle. He began to tell his story.

"You all know about the avatar, right?" he asked.

"I am the avatar." I said.

"I am fully aware of that. That is why I will tell you four the full story. A-a-and you…the avatar, you can help." he replied.

We all looked at each other curiously. The old man bowed his head as he sat cross legged, and he attempted to make a fire, as it was approaching night time. I helped him by just making a fire out of nowhere. He sighed, and then nodded in my direction.

"As you may or may not know, the avatar is one person. When he or she dies, he or she is reborn into a new body, and a new element." He explained, taking a few pauses to cough. "Well, the rumour passed down my family, is that long ago, when the very first avatar was born, they had a brother."

"I-I've heard about that," I said, looking down, playing with my thumbs. "In fact, I was there. I may not remember it like it was yesterday, because in reality, it was millions of years ago. My very first creation; her name was Avatar Fang, born under the element of air."

"That's right. But more importantly, the Avatar had a mortal family." the old man replied.

"Aang, you had a family? How come you've never told us?" Katara asked.

"It just never came up, I guess." I replied.

"Anyway, the real phenomenon is that Fang's family of mortals had one bender. Now Avatar Fang was the first to introduce the earthly and natural elements to the world, air, water, earth, and fire." He stopped to cough. I noticed that he coughed out what seemed like dust. Clearly he was very poor. "Anyway, because of this, her brother was a bender that bended none of those elements." he said.

"What other elements are there?" Sokka asked.

"Well since this man was the opposite of Avatar Fang, then he bended the opposite elements." the old man explained.

"The opposite of earthly natural elements, would be elements related to science and technology, right?" Toph asked.

"Correct." the man said, drawing four unique symbols into the ground. "The four elements this man was born with, were the elements of science and technology; sound, electricity, steel, and plasma."

An awkward silence passed. By now, it was near midnight, so we couldn't really see each other well, but Katara was able to see the look on my face.

"Aang…what are you thinking?" Katara said.

"I have to meet him. He's my brother." I explained.

"Remember 'he' could be a 'she'." Toph said.

"How are we even sure this guy's legit? He's wanted by the Dai Li!" Sokka exclaimed.

"Shut up Sokka, he's right there." Toph replied.

"If he was really talking nonsense, the Dai Li wouldn't care what he did." Katara explained.

"Think what you want, but now I tell you, it is not a myth. Just as the Avatar is reborn when he or she dies, so was he. The story my grandfather told me, was that there is an organization on the other side of the Avatar world which runs on technology and computers." he said.

"Guys, can we go now? I'm hungry…" Sokka admitted.

"Sokka, don't you know what this means? There's someone out there who's just as powerful as Aang!" Katara exclaimed. "If they wanted to, they could be a serious threat to the Avatar world."

"That must be why the Dai Li didn't want the news to spread!" I replied.

"The real question is, what do the Dai Li have to do with any of this?" Toph asked.

We all exchanged looks.

"So what is he anyway, an Avatar?" I asked.

"On the contrary." The man murmured. "He's the-the Ratava."

"What kind of jacked up name is Ratava?" Toph remarked.

"Speaking of names," I said, "what was his?"

The old man put down the twigs he was playing with, and looked up at us.

He gave it a long hard thought, and said, "I don't remember. Actually, I don't think his name was part of the story, I never asked."

"I remember." I announced. "His name was Yin. Ratava Yin. At least that was his name a million years ago. I have no idea who they are now."

"I never thought that I would say this, but Sokka's right. We need to leave, now." Toph announced, jumping down onto the floor, feeling the ground with her palm. That was when she looked up at us, with a serious facial expression. "There's a large amount of footsteps heading in our direction."

"One quick thing," Katara said.

Suddenly, a bright light lit up the alley. We turned around. It was the Dai Li. They pointed at us, and shouted commands.

"Where can we find this world?" Katara shouted through the ruckus.

"You will have to travel to the other side of the planet. Much farther than a small trip to the air temples." He said.

At this time, the Dai Li were running towards us.

"I'm sorry, but we have to get out of here." I said, nodding to the old man. "Thanks again."

I held out my hand, and Katara, Sokka, and Toph held on. We dashed straight up into the air, avoiding the Dai Li. Serendipitously, Appa was not far away. He picked us right up, and we looked down. The Dai Li were pointing at us. Clearly, the information this old man was telling us, had some kind of importance. Something the Dai Li couldn't risk releasing to the public.

We were officially fugitives.