In a world that is unbalance and filled with such hate. The creation of the universe is so unbalanced and filled with war and chaos but it also part of the underworld and that is probably being evil and also fill with fear, despair, and also anger.
Heaven realizes that it is the other of the underworld and that is peace and kindness but that is told in the story but we never know if it true or not but that is something that is part of the universe created and so they had made it to where they had made divide it to light and darkness.
There is a balance between the two and that is called the Yin and Yang and that is something that can be described as such as their light in the darkness and then there is darkness in light without the two of the systems then there will be no way that the universe can become in the light and darkness.
"Sister, I wonder why mom is so mad at me?"