Disclaimer: I do not own Kingdom Hearts; it belongs to Disney and Square Enix! I only own this story!
In ancient times the world was enveloped in darkness. Great wars, bloody fights and difficult conflicts took a huge amount of lives in the once peaceful community. This was partly caused by the citizens' individual beliefs or other plain and everyday differences. However, the main reason behind the wars was the sudden power development caused by the origin of the Heartless.
The Heartless' creation was, according to the legends, caused by a failed attempt at creating the perfect SOLDIER for the government. An explosion caused by carefully chosen and rare, radioactive chemicals resulted in the Heartless being painfully forced into existence.
The incident took place in a lab, which was used by the world's most qualified group of geniuses and scientists. But, because the project to create the SOLDIERS was by far the most secretive and important project ever started by the government, the lab was placed underground to prevent sabotage and espionage.
The level of secrecy also resulted in a very small group of scientists, so they could prevent the word from spreading like wildfire on a dry field throughout the world in the media.
In the lab the only living beings were the 4 scientists working on the project and the first person chosen to become a SOLDIER.
During the explosion they all became Heartless. Depending on how far away from or how close to the chamber they had placed themselves, their strength and rank of HEARTS decreased or increased as a result of the amount of radioactive chemicals absorbed in their veins.
The SOLDIER candidate, Ventus, absorbed the greatest amount of the deadly chemicals and thus also received the highest rank of HEARTS. He became a Nobody.
After the explosion the rumours started spreading like it had previously been predicted to. In the end the government decided to send in a group of special trained, young troops to investigate the laboratory and thereby assuring the citizens of their future safety and normality.
The troops that had went underground to investigate the matter never returned.
When it was evident that the young troops would not return to the society the government closed of the entrance to the former secret laboratory.
No one could have possibly known that what the troops found in the destroyed laboratory would be the beginning of a long war that was going to cost uncountable amounts of blood and hearts...