In the beginning, while the earth was still young, there were always two types of creatures. Creatures of the Light, and creatures of the Dark. Each are made of concentrated Light magic, or Dark magic.
Creatures of Light have many other names, such as Lightlings, the Light, and the Light People.
Creatures Dark have other names as well, such as the Dark, Darklings, and the Dark People.
When a Light and a Dark touch each other, 2 results may occur.
If one creature's soul is stronger than the other, then the other creaure's body will cause the other's body to break apart. The one with the stronger soul will not feel any pain, but the weaker will suffer tremendously, as they slowly dissolve.
Or, if their souls have equal strength, then both will begin to dissolve, as long as both are still in physical contact.
What defines a strong soul? A will to live, hopes, dreams, and believing in oneself.
Creatures of Light draw power from the sun and other light sources, such as fire, but mainly the sun. Without the sun, the Light's powers are weakened. This makes them vulnerable in the night.
Creatures of Dark draw power from moonlight and shadows, but when in an abundance of light, the Dark's powers are weakened. This makes them vulnerable in the day.
Some creatures of the Light can dissolve into light photons, losing all of their physical matter. This "photon form" acts like a hologram, and they can come out of this form and regain their physical matter once again.
Aome creatures of the Dark have a similar power, except they can turn completely 2 dimensional and turn into a shadow of themselves, as long as there is something behind or under them to cast a shadow on.
The bodies of each creature contains their soul, as well as magic not fully condensed into solid matter, mostly in a liquid form. This acts as the creature's blood.
As time goes on, the light in creatures of Light slowly dim. It is a slow process, but eventually all creatures of Light will fade out of existence, and die. The same happens to creatures of Dark. Over time, a creature of Dark will slowly lose their darkness, and they will slowly "fade out" and die.
This process is known as "the fading" and takes several years, decades, or even centuries, depending on the creature's lifespan.
If a creature dies of causes other than the fading, then their bodies will simply become less and less opaque until you cannot see it anymore. Basically, a faster fading. This process itself is not painful, however the cause may be, such as disease, body trauma, or bleeding out.
It is said that there are certain creatures that cannot fade due to old age. These creatures are known as "Eternals" and they are theoretically immortal. It is unknown how these creatures can achieve this, or even if they exist at all.
Some Legends speak of Eternals giving life to other creatures; adding darkness to a fading darkling, or adding light to a fading lightling, prolonging their lifespan. These Eternals, however, only exist in legend, and it is unknown whether or not they truly exist.
Some worship these eternals like gods, others reject their existance, claiming they are simply myths.
While most creatures of Light and Dark live in the wild, others became more sapient and created civilizations. These creatures are known as Citizens of the Light, or Citizens of the Dark. These creatures banded together to form the 2 Kingdoms of Light and Dark.
When creatures of this world breed, it does not matter what gender either partners are. (Both creatures of light and dark have no genitalia. They reproduce completely differently and more wholesomly.) When two creatures wish to reproduce, they hold hands, and perform a dance. After this dancing ritual, their physical matter dissolves and they convert the entirety of their bodies into dark or light magic (it doesn't matter what type of dance they perform or how they dance, as dancing is only a way to express themselves). They then fuse and become one, and meld together into an amorphous sphere. Their souls will fuse together, and then, it will split into 3 souls. 2 are the original souls of each partner, and one entirely new soul, the offspring's. The union is then split, and everyone is back in their original forms, in their own separate bodies. The child will then be encased in an egg, to be cared for by the parents. This entire process can only be done if both partners truly wish to give their consent.
Due to the nature of light and dark creatures, it is physically impossible for a light and dark creature to breed together. They simply cannot come in contact with each other without destroying one or each other.