Apart from the baseline humans, Ghosts and Mosnters that populate the setting there are three driving races the Demon, the Leviathan and the Angel.
First up is
Demons, they are human spirits that have been permanently changed/empowered at the cost of becoming corrupted and malevolent. The most common beginning for a demon is that of a soul dammed to Hell (either by sufficient evil action or by making a bargain with a Demon) where via torture and spiritual pollution by the essence of Hell they are transformed into a Demon. Other ways to become a Demon exist though they are rarer.
Demons are in regards to dice and abilities essentially abnormally powerful Ghosts who do not have to worry about Spiritual Decay while active on the Mortal Plane. However their are some differences from baseline spirits, Demons are inherently parasitic requiring to possess a human host to make their will known on the Mortal plane in contrast to Ghosts who can communicate and manifest without a physical body. Their are many types and categories of demons.
Next are the
Leviathans, the Oldest of the Old, the First Beasts. The Leviathan are primordial lifeforms that are nigh invulnerable and highly versatile. They are also insatiable, hyper aggressive carnivores that see anything and everything as food and are alarmingly intelligent. They are (or were) locked away from the rest of creation in the place known as Purgatory where they endlessly preyed upon each other.
At the dawn of human history a lone Leviathan found its way to Earth and bred with certain humans creating the various bloodlines of monster's. All monsters that walk the Earth are descended from the Leviathan's and when they die their souls rather that ascending to Heaven or falling into Hell go to Purgatory. Leviathans are to normal monsters what monsters are to humans.
Lastly are the
Angels, they are the agents of Heaven, beings forged of Divine Energy and in essence the Children of God, albeit far weaker than their all powerful father. Angels are capable of numerous feats ranging from teleportation across continents to fine tune bio alteration. The true form of Angels are titanic things of Light and fire, taller than buildings with voices louder than than thunder, utterly alien to human ideals of form and life. For one not of the correct bloodline to look upon the true form of a Angel is to have the eyes burned from their head.
Angels acting out of a desire to avoid the complete collapse of human society take mortal vessels to operate on the Mortal Plane, but unlike Demons are perfectly capable to acting without a human body if they so desire. Their are many orders and kinds of Angel.
Sidenote: In this take on the setting, Amazons are descended from the Leviathan same as all the other monsters. Ares and Harmonia were creatures of Purgatory that reached Earth and ruled as gods. They agreed to transform the Amazons for much the same reasons that Eve made the other bloodlines.
If you have questions please ask and I will try to answer.