Life and death. Harming and healing. Magic is based on these concepts, and must be balanced, equal, stable. This is the basis of the world that many sapient species live in. There are nagas, mermaids, garuda/harpy, fae and humans (and other).
The primordials(/gods?) were upper half human, the other half godly, and so they each passed themselves on to a different type of creature; the apes(mammals), the fish, the snakes (reptiles), birds, insects, (and amphibians). This resulted in the species present now.
The world is similar to ours: a main sequence sun, similar size and temperature, the planet is the same size and its mechanics the same but magic is present. Each sapient being can use it.
There is a second dimension to Dayira, and where there are beings of that realm. They are unlike those on Dayira due to lack of a soul. If a soul of a Dayiran is taken by one of these Greater Demons, then the being is trapped in that realm. It can no longer perform magic and are under the control of the being who owns their soul.