Thousand years ago, the 22 ruler Gods of the World battled with each other. 「The Great War」 to obtain the right to hold the 「Highest Authority」 of the World, as well as to win the heart of countless followers and worshippers.
In a more concise term, the Gods of this world were too easily to provoke, childish, and selfish.
「The Great War」 led to the 「Order」 and the 「Chaos」 of the world fell apart, which caused many of the creatures of the World killed and tormented.
They attacked each other, tortured each other, and destroyed each other. But even with those damages they were still could not die, because of their title as the "Gods". On the cusp of their conflict, their endurance as "God" dwindled due to the war that ensued. If they keep the war on, they would become powerless, as weak as human beings. Therefore, they decided to postpone the continuation of 「The Great War」 in the future.
Since then, the entire 22 ruler Gods of the World fell asleep, rested to recharge their power, prepared for the second half of the 「The Great War」.
To keep the World they ruled descended into the 「Pandemonium」, the 22 ruler Gods of the World leased their almighty power to the 22 「Chosen One」. Or in a more precise term, the 「Unlucky One」, since the Gods were in a haste to go to sleep and had no time to choose with care. This almighty power from the Gods will pass down to each generation, excogitated a string of endless chains to hold the World from the 「Endless Chaos」.
In fact, the days without the supervision of the Gods caused even more 「Chaos」 around the World. The 「Chosen One」 —holder of the godly power—could not cope with the crisis in every area. Useless wars and conflicts were spread and escalated, resulting in similar conditions after the end of the world, after the apocalypse. It was a period that lasted after 「The Great War」 of the Gods, a time when humans were able to control the powers far beyond common sense: 「Black Age」.