Outside of perception exists a realm of gods. This plane has existed ever since the creation of concepts. Throughout the realm, there are being which supervise these concepts. For mortals, they can be considered as gods. A single god can have others as their subordinate/s. A good example of this would be the God of Origin who presides over every single god that ever existed.

Then comes the God of Sin. Along with him, his 7 familiars and 2 gods.
The Seven Deadly Sins as his associates and the God of Death and the God of Murder as his equals.

However, the God of Sin has a single problem. The Lord of all Sins, The Holder of the Original Sin is such an expressionless and a very indifferent individual.

Planning to fix this, the 2 gods concocted a plan where the God of Sin would be stripped of his characteristics as a god and be casted down towards a world where he can experience first-hand the sins he's presiding.
Of course, they had to ask for help. No one other than the God of Origin. He approved and stated.

"Very intriguing. I wonder what he'll become."

Thus begins the story of Sin, on a sinful world.