Hystoria is a world rife with monsters, but it was not always so. The gods who created the world originally made it without monsters. They made the many races to inhabit the planet and live in harmony. However, one god was shunned by the others and not allowed to create what he wished in the world. In response, he created monsters in secret, and set them loose to terrorize the other gods' creations. The other gods were furious when they found out, and imprisoned this god in a prison that could never be opened. Unfortunately, they could not undo what the evil god had done, and so, the monsters were unleashed upon Hystoria.
Centuries passed, and the races banded together in cities to protect themselves. Among the cities, there were those who chose to aid in the fight against the monsters by accepting contracts to kill them. These brave souls were known as adventurers. They formed guilds where the general populace could post jobs they needed doing, monsters they needed slain, and the adventurers would answer the call for a fee. Many adventurers gained great renown for their deeds. With the aid of the adventurers, the monster hordes were pushed back, and civilization flourished.
The monsters were held at bay for a few centuries, until one day, they grew stronger, seemingly overnight. Suddenly, they seemed smarter, more vicious, and more organized. This was concerning, so adventurers were tasked to investigate. They found that the monsters themselves had not changed, but someone was leading them. A sorcerer known as Ainz Ooal Goan had taken control of the hordes and was using them to try to eliminate civilization and remake Hystoria entirely. Many adventurers had tried to kill him, but all had failed. 20 years passed before a legendary group of adventurers, called The Occult Research Club, managed to unite the cities against him and slay Goan.
That was 30 years ago. In the time since, the world has calmed, the monsters being pushed back and civilization flourishing. It is an era of prosperity and relative peace, but there are stirrings in the shadows. Peace can never last, and it is only a matter of time before Hystoria is once again in need of heroes to save it.