Disclaimer: I do not own Avatar or any characters mentioned nor do I own Kingdom Hearts or any characters related to it. (c) Square Enix and Nickelodeon and their respective creators.

Lightning, Air, Water, Earth, Fire

Long Ago, Avatar Korra managed to stop Amon and the Equalists and put an end to the long lasting anti-bender revolution. However, like after any other war or revolution, there were still a few rebels who wanted to continue Amon's plans, but to no avail. Instead, they held a grudge against all benders within themselves and it manifested into a dark energy within the hearts and spirits of people. This darkness was eventually passed on to the next generation and in time, it grew in size with Avatar Korra being completely unaware of the situation. After the death of Avatar Korra, a new avatar from a small town in the Earth Kingdom, Terra was born.

During Avatar Terra's time, his greatest obstacle in creating a once again peaceful world was the dark energy that existed within people. He discovered that the dark energy from Korra's time was not only composed of those who hated benders, but was also of those who still held a grudge against non-benders. Eventually, a dark spirit, who was later named Yami, was born from all the darkness that had accumulated over time. Its total black and tall appearance alone would send people running in fear. However, when it was to reveal its hidden face to humans it was said that they instantly died as it removed their spirit from their bodies where Yami was to later consume it. Ultimately, after gaining much more power from the consumption of human spirits, Yami produced his own minions who were later dubbed as Grudges. They were creatures that were smaller than your average human and black in appearance with a dark aura silhouette surrounding the contour of their bodies. They went off attacking other small towns.

Avatar Terra finally became aware of the situation and took it upon himself to put a stop to Yami and his destruction. It was there where he gathered the best benders and warriors from all around the globe and took on Yami and his army head on in what would later be called the battle of Grand Fissure. It was a desert terrain with giant rock columns sprouting all over the place. It was located in the middle of the Earth Kingdom in an area known as the Keyblade Graveyard. Terra and his army put up a formidable fight destroying more than half of Yamis forces but Terra's side was also suffering its own losses. In the end, Terra realized that his forces would be exterminated if they continued fighting in their current state so he decided to sacrifice himself in order to save the world. With the power of the four elements, the spirits of the previous avatars and the energy present within his own spirit, Terra managed to seal the almost undefeatable Yami within himself and with this, the rest of Yamis forces also disappeared. Benders and non-benders alike rejoiced in the defeat of Yami and the peace that pursued was known as the Great Calm.

However, Avatar Terra's health was deteriorating as the amount of energy needed to suppress and contain Yami was taking a toll on his body. Yet, his understanding was that even if he were to die he believed that Yami would die with him, but that was not the case. Unfortunately, Avatar Terra passed away with the false hope that Yami would die with him, at the age of 38 where legend has it that his body was equivalent to that of a 185 year old. Immediately after, a girl from a multi-racial family living in the Fire Nation, Aqua was born.

In her youth, Aqua was often teased for her name as it meant "water" which contradicted both her style of fighting (firebending) and the place in which she lived. She was named Aqua due to her father being a descendant from the Northern Water Tribe and his strong belief that he and his Fire Nation wife's first child should be named after something relating to water despite the possibility of her being a firebender. However, little did her peers and parents know that she aswell would turn out to be a waterbender, an earthbender and an airbender. Anyways, during Avatar Aqua's time she realized that something was different about herself and it was not something mentally, physically, or emotionally but spiritually. She then decided to visit the spirit world in the hope that a wise spirit would be able to assist her in her time of need. However, she soon discovered that remnants of the once thought to be destroyed Yami, lingered on in the spirit world and that these fragments were slowly but surely slipping back into the human world. She then encountered Avatar Terra and a hybrid of a monkey and an owl looking spirit called Who. She was told that the only way to stop the fragments of Yami from re-entering the human world was by creating a seal between the two worlds in which only the avatar should be able to break. However, in doing so, the fragments of Yami would try to fight their way through the seal in an attempt to break it and the only way to prevent this was for Avatar Aqua to remain in the spirit world and protect it.

After much thought, she went against her husband Igneous' wishes and entered the spirit world with a specially crafted sword known as "Rainfell" as her means of fending off the Yami menace. Behind, she left her husband, 4 children (Neptune, Zexion, Vincent, and Satoshi), and her people in order to prevent another event like the now called "Dark War" from happening again. With her body remaining in the human world, it was tended to and protected 24 hours a day, 7 days a week. During her absence, her children and husband took on her role as protector and peace maker of the world by traveling across the globe promoting peace and helping those in need. Eventually, like any other mortal, her body gave out in the human world thus forcing her spirit to return to her body. However she did leave her seal protected by the strongest of sprits around and was confident that her efforts would not end in vain. She passed at the age 93 with her immediate successor being born to a couple whose ancestors originated from the Air Nomads. This child was named Ventus, but friends and family lovingly referred to him as Ven.

(Now before continuing with Ventus' story, during Aqua's absence from the human world a sixth nation was established and was called the Lightning Empire. The nation was in progress from early on in Avatar Terra's time as the gene for lightningbending soon became its own instead of being a subset of firebending. Over time firebenders soon lost their ability to lightningbend and lightningbenders soon lost their ability to bend fire. During Avatar Aqua's time, it became an official requirement for every and all avatar's from Aqua and onward to master the art of lightningbending.)

Avatar Ventus, was unlike other Air Nomad originating Avatars as he did not follow their customs or traditions such as shaving his head as his parents never pushed nor stressed the importance of his heritage and he never took a major interest in it as well. By some he was considered a disgrace of an Air Nomad but that never affected him as he was later known as one of the greatest Avatars of all time, albeit way after his death. When Avatar Ventus was informed on the seal created by his predecessor Aqua, he was told that he should visit the spirit world himself to check on the status of the seal and if the seal looked as if it were about to break, to reinforce it with his own stronger energy. However, much to his dismay, he found the seal broken and also found the rotting carcasses of the spirits that were supposed to protect it until the return of the Avatar. One spirit that did survive, a griffon looking spirit called Taka, informed him that the seal had broken only 5 years after the death of Avatar Aqua. This meant that the seal had been broken for over 19 years and that the fragments of Yami had completely infiltrated the human world and are once again within himself. Knowing that with his death, that Yami would once again return, he traveled across all the six nations and trained the most elite of benders and non-benders alike in order to be able to defend themselves until the next avatar is old enough and strong enough to put a true end to Yami and bring upon true peace once again. Also, in order to ensure that these newly trained benders were up to par and that the generation after them also had the ability to defend themselves, Avatar Ventus set up an organization called "Organization XIII" which was composed of his closest and strongest bending and non-bending friends from across the world. However, in order to prevent the organizations members from abusing their power, like with the Dai-Li during Avatar Aang's time, he set up powerful judicial system known as the Great Justices, to judge and ensure that power was not being abused not just within Organization XIII but with controversial cases all around the world.

The Great Justices was composed of 2 representatives from each nation, one being a bender and the other being a non-bender, with a head judge known as the Grand Justice being the tie breaker in the case where a tie was to occur. This Grand Justice would change every year to a bending or non-bending representative from each nation every 6 months. The rest of the justices served terms of 5 years each. Finally confident that the world was ready for the impending war, Avatar Ventus passed with many despising him as they believed that his efforts were in vain for they thought that the seal had never broken and that he used the lie in order to impose stricter rules and spread his power over the world. But as previously mentioned, he was later praised for his efforts.

Then, Avatar Xehanort of the Northern Water Tribe was born. During his late teenage years Avatar Xehanort was confronted by a weak Yami who barely managed to survive the years he spent in the spirit world during Avatar Aqua's time. Xehanort was promised absolute power and dominance over the whole world if he were to accept him within his body but not as a contained spirit but as an extra boost of power where a symbiosis was to take place. Avatar Xehanort enjoyed the idea of being able to dominate every and all persons living in the world as many of them had lost their respect for the avatar despite the many good deeds that past avatars have done. Therefore, Xehanort allowed Yami to live within his body where Xehanort created his own minions whom he dubbed Heartless and began his desire to conquer the world. The heartless were less menacing looking creatures than the Grudges but they came in a wide variety of shapes, sizes, and different bending capabilities. Xehanort caused mass destruction across the world including his very own home. However, Avatar Ventus' efforts did prove to be very effective as these trained warriors were considered to be very formidable opponents against Xehanorts forces and prevented further destruction from occurring.

All past avatar's were displeased and infuriated with the actions of Avatar Xehanort and they took it upon themselves to end Xehanorts life by killing him from within himself. And so the many past avatar spirits appeared before Xehanort in a flash of blue light where in unison they spoke, "You have caused great pain far and wide and for committing such a crime you are revoked of your avatar duty." It was here where Xehanorts spirit was removed from his body and his immediate successor Avatar Vanitas was born to a family in the Earth Kingdom.

The world had hoped and prayed for the new avatar to finally be able to make amends and properly fix the world whereareas his previous reincarnations were unable to. But much to the world's dismay, the still existing Yami spirit along with Xehanorts spirit corrupted the young mind of Vanitas and instilled all of his predecessor's goals within his own mind. Vanitas caused ten times more destruction then Xehanort could have ever dreamed of. It was said that he wiped out a quarter of the world's population in a matter of 8 months. However, like with Xehanort, the avatars banded together once again in order to put an end to another reincarnations life and they ensured that this time the next reincarnation would not be corrupted and will continue the true purpose of the existence of the avatar. However, as a last ditch effort, before Vanitas was to die, he along with Xehanort and Yami split all of the avatar spirits in half causing each half to be reborn into two separate children. These children are the ones in which the main story will take place and their names are Avatar Sora of the Fire Nation and Avatar Roxas of the Air Nomads.

With the existence of two avatars at the same time, the human world and spirit world as we know it is fading. The human world crumbles away with once luscious forests being converted into deserts and the poles melting back into the ocean. In the spirit world, it has slowly begun to fade with many spirits as well fading from existence. It is up to Avatar Sora and Avatar Roxas to sacrifice one of themselves and merge with one another in order to bring the past avatars back together and face off against Yami, Xehanort, and Vanitas and destroy the dark energy within them once and for all.