1. Overview of the world
Before the very first Master of the Nine Tribulations Sword, a man was responsible for the current state of the Nine Heavens Continent. The Nine Heavens Continent was originally a single piece of land. That man used the Nine Tribulations Sword to reform the Nine Heavens Continent, separating it into nine equal layers (each race occupying their respective layer, with the Human race at the very top). However, those nine equal layers turned out to be unstable, resulting in the collapse of the top eight layers, crushing a huge portion of living creatures beneath them (also causing some races to disappear from the Nine Heavens Continent). Since Humans mostly resided top layer, they therefore became the most common living species on the Nine Heavens Continent.
Following that disaster, that man once again used the Nine Tribulations Sword to reform the nine layers, which resulted in the current state of the Nine Heavens Continent — Lower Three Heavens, Middle Three Heavens and Higher Three Heavens. The Lower Three Heavens is the smallest layer, while the Middle Three Heavens is slightly larger than the Lower Three Heavens. The Higher Three Heavens is the largest of the three layers. After that, the man separated the Nine Tribulations Sword into fragments across the Nine Heavens Continent, and left.
It would later be known that the man came from the Nine Heavens Palace, which is a realm beyond the Nine Heavens Continent.
Examples of races which disappeared during the disaster include the Dragon race, Phoenix race, and Elf race. Races such as the Demon race and the Three Stars Saint Clan (which is a race of Lesser Devils) were sealed by the mysterious man in an unknown part within the Nine Heavens Continent before he left. The seal would begin to weaken as Masters of the Nine Tribulations Sword progressively find the sword fragments.