From the introduction:
The World of Conclave is a world rich in spirits that run the machinery of the world at the behest of the Immortals. Stars shine in the sky because they are lit and tended by star spirits. Flowers bloom because they are given life by plant spirits. Rivers ebb and flow at the behest of river spirits. Everywhere, the invisible servants of the Immortals ensure that all works as it should. Not all spirits are benevolent. Madness spirits can possess an unfortunate mortal and drive him to acts of insanity. Disease spirits cause sickness. Hostile creatures from the Underwater Darkness World sometimes cross over to the mortal realm to cause mischief, such as Mirror Spirits who can take over a person’s reflection to form an evil double.