When the Tower of Babylon appeared in the world of Hestia, many people believed that it was a tower that had been built by Gods.
Back then, a declaration was heard by every living thing in the world, asking them to challenge the Tower and seek the riches that were hidden within.
This story happened a thousand years after the Dark Era of Humanity. Since then, millions of people have made a pilgrimage to the tower to seek fame and fortune. Many failed, and only a select few succeeded.
Each floor was supervised by a Guardian. Some called them Deities, some Administrators, and some simply called them Gods.
The people who had first cleared the floors made a contract with these Guardians, and became the rulers of the Domain. Naturally, they were also there to reinforce the rules that the Guardian had set, and allowed the others to challenge the tower.
