Mankind.
Are sent to the world as we know of because of their unloyalness to their god. It is deemed as a punishment, yet a test of redemption to never make that same mistake again.
Likewise, even though some people remain loyal to their holy god after being thrown out away from the heavens, it seemed that more people started to throw their beliefs away from themselves, as the demons who too, got sent to the earth, make those humans forget themselves. And as time passed by, they began doing awful things. Harem, slavery, killing. These are the actions that they made and all of it was getting worse the more the world went, as a matter of fact, some of those people who are loyal to the holy god usually didn't give their teachings to their children in strict ways to make sure they are deemed loyal, hence make them turned into those who went into the dark path. All of this continues to remain worse.
It was at that time when 'The Reminder Of The Heavens' was sent to Earth for the first time, as the world became lost on its own. The purpose of these figures who came in one by one for every era is to remind them to be on 'The Straight Road', a road that will lead to their happiness if they obey their god.
 Of course, at first, the world is enraged with their actions because those figures were prohibiting the world from doing sins, something they like, but as time goes on they will soon later learn to accept it and become a part of it for their lives.
It was soon then that the world was deemed safe to those legendary figures, which led them to leave the world alone again as God ordered them to only remind them, because of it, The Reminder's era suddenly came to an end, as the last reminder conclude that there will be no more of them yet, as the world has been reminded by them with many holy books sent to them as an addition. The world, although saddened, waved their final goodbyes to their last Reminder as his breath faded away.
 It was at that time that the world experienced balance, although some people still did not obey their god, after all, one of The Reminder's Legendary Quotes said that evil was impossible to contain, so it was not rare to see them.
Of course, after that, the world will have two sides, the good and the evil within, but the evil might finally manage to get their world back as one man, become the leader of them. It was so threatening to the world, that some speculations said that there would be a new Reminder for them after thousands of years. It was soon or later that the world was either in both side's hands.
This is just the beginning...
Of an end.