Chapter 1: Mad Science

Water, Fire, Earth, Air. These four elements make up the art of bending in each of the four nations, for thousands of years they lived together in harmony, but that all changed when the Fire nation attacked, starting a war that lasted a hundred years. The only one who could stop them was the Avatar, the master of all four elements. But unfortunately, he had disappeared and didn't reappear until a hundred years later.

The Avatar, an Airbender named Aang, appeared when the nations needed him most and defeated the Fire Nation with his friends. Now the world was at peace and was trying to readjust. But little did the nations know, however, that this newly crafted time of peace would soon come to an abrupt, and violent end.

-Fire Nation capital, Palace of the Fire Lord-

The Fire Nation was now trying to recover and in turn help the other nations recover as well. Their new leader, Fire Lord Zuko, was being very adamant about this goal. He had promised his friends and himself that he would redeem his nation in the eyes of the world, as much as he could.

Zuko was the son of the previous Fire Lord, Ozai, and was previously disgraced and even burned by his own father, so he had a scar on his left side of his face.

As Zuko was working on various policy adjustments with his advisors, a messenger came into the room with a really panicked look on his face, sweaty and gasping for breath.

"Fire Lord Zuko!" The messenger gasped as he held out a scroll. "I have an urgent message from Ba Sing Sei!"

Zuko looked at the messenger as he took the scroll. As he read it, his eyes widened in shock. Putting down the scroll, he looked at the man seriously. "Has Avatar Aang been notified?" He questioned.

"Yes Lord, a messenger hawk has been sent to his residence at the Northern Air Temple." The messenger nodded.

"Good, leave us." Zuko ordered as the man left. The boy looked at the scroll and read it over again. Just what was going on in Ba Sing Sei?

(Meanwhile at the Northern Air Temple)

At the Air temple, there was a new herd of Sky Bison flying in the sky and several new lemur bats as well. A sign that they were recovering. In the temple itself a young boy was seen meditating in silence. A few minutes later, however, his silence was interrupted by the cry of a bird as a messenger hawk flew over him before landing next to him.

The young man tried to play it off as he continued to meditate, but unfortunately the hawk kept pecking his arm to get his attention, so he sighed and faced the bird.

"A messenger hawk?" The boy asked as he opened up its pouch and pulled out the message. He read it and slowly his eyes began to widen. "Oh no…" He gasped as he ran towards the temple's middle area. "Katara!" Aang called out.

As he ran towards the center of the temple he saw a brown skinned girl with beautiful brown eyes and ebony black hair styled in a braid and two hair loops. She was busy trying to clean the temple walls with water bending. As he ran up to her, she turned and smiled as she saw him.

"Hey Aang, what's… What's wrong?" Katara asked as she saw the look on his face.

"I just got a message from the Fire Nation, something's happened in Ba Sing Sei, and from the sound of it, it's big!" Aang said as he read the message again. "They found some kind of underground room that had been sealed off after the war had stopped, and they need me to help investigate."

"That sounds pretty big. Do you need me to come with you?" Katara asked.

"Normally, yeah I would, but in case things go south I want you to be safe." He told her, grasping her hand.

"Alright, but be careful okay?" She requested squeezing his hand.

"I will." He nodded as he pecked her on the lips before leaving. He ran to the ledge where he previously was and jumped off, then whistled as his Sky Bison, Oppa, came and caught him on his back. "Oppa, Yip Yip!" Aang ordered as they flew into the sky.

(A few hours later in Ba Sing Sei)

Aang arrived at Ba Sing Sei rather quickly and landed outside the wall. As he dismounted he was then met by Zuko who had also gotten there quickly because of his own ride, one of the newer dragons that he helped breed.

"Zuko!" Aang said as he ran up to the older man. "What's the situation?" He asked as he hugged his old friend.

"Well, according to the few scouts who were able to get in, they found some sort of abandoned room. The new scientists you provided us, they said it looked to be an old and abandoned lab of some sort." Zuko explained as they entered the city.

"A lab?" Aang asked in confusion.

"A place where scientists do experiments. But the strangest thing is that there's a large glass cylinder of some sort in it. We're not exactly what's in it, but we can definitely conclude that it's at least human." The young man explained.

"A human experiment?" Aang questioned with a disturbed look. "That's Just...wrong."

Zuko nodded as they came up to the giant hole that had resulted from when the lab was first discovered. The two jumped down and Zuko discarded his robe, revealing he had on his combat clothes and dual swords on him.

Aang gave him an incredulous look. "It's for if we run into trouble." The fire bender defended as they descended into the tunnel. They kept walking until they reached the lab, it was composed of carved stone and the walls were covered in pipes and different control panels were everywhere, notes were also strewn all over the floor, and in the center was a giant tank full of odd green liquid.

As Aang picked up the notes, he read them briefly. "Project Black Demon?" The Air Nomad asked with a confused expression.

Zuko looked at a few other notes. "According to these notes, this used to be a lab that belonged to a scientist who was working on a project that involved something called 'Genetic manipulation'."

"What's that?" Aang asked.

"According to the notes? Forcibly modifying someone's genetic code, or what makes them who they are, to fit certain criteria." Zuko explained while reading more notes, before getting a grim expression. "And it looks like that's not all they did."

"What else did they do?" Aang asked, dreading the answer.

"Apparently, they stole the essence of a Dark Spirit they captured and fused with the subject, basically making him part spirit, kinda like…" Zuko explained before looking at his friend. "The Avatar."

"Wait, what?!" The Avatar gasped in shock, backing up.

"That's what it says. And according to the notes the subject has the blood of both Fire benders and even Lighting benders mixed in it. This would, I assume, mean that it's able to use two elements." Zuko explained as he crumpled the paper, before growling. "And the genetic material they used was from my own family line, though it's unclear exactly who since the rest of the notes are damaged." He then walked up to the tank as he looked at it. "Meaning this, 'Black Demon', is basically a part of my family."

Aang was unable to stop himself from stumbling back in shock before he accidentally placed his hand on a control panel and accidentally pressed a random button. That's when the lab's systems suddenly activated and the tank's green liquid started to drain and it then opened as the body of the boy fell to the ground.

The person who was in the tank was a boy around their age. He was a boy who was 5'9" with black hair, fair skin like Zuko, and had a similar build as the Fire Lord as well, his body was covered in odd tattoos too, on his right side he had black flame tattoos and black lightning on his left side that all went from his arms to his abdomen. Both young men looked at the body as Zuko quickly put his robe over him.

"Do you think he's alive?" Aang whispered.

As if on cue, the boy then drew in a deep breath and started coughing as he slowly tried to get up, wrapping the robe around his body. Seconds later the boy opened his eyes, revealing them to be a burning red and were sharply angled like Zuko's.

"Does that answer your question?" Zuko whispered back.

The boy groaned as he held his face with one hand. "Wha... Where am I?" He asked in a voice which was also similar to Zuko's.

Aang was going to say something but then the boy looked at him and then his right eye was then set ablaze with unnatural black flames.

"Avatar…." The boy growled as he stood up, and then he outstretched his right hand in front of the two as it was engulfed in black fire. "Be gone!" He yelled as a blast of black fire went straight towards their targets.