Demons

Demons are hugely diverse, but still somewhat related to the Caelia. They exist in the same realm of the caelia, but are somewhat lesser beings as their reach of power is more limited. Instead of having large influence on the natural world, they interact on much smaller scale, usually targeting specific beings.

Demons can haunt the living by entering their dreams, pull their soul into another realm. They tend to be weak and not be able to harm the soul at all, just subject it to psyche attacks. After a haunting, the consciousness of the soul returns to the physical shell with the memories intact.

Amongst this diverse group, there are some very powerful demons that can enter the physical realm through rituals and through the body of willing hosts. These tend to be extreme examples and not many recorded instances. Often, only influencing the host's actions through suggestion and manipulation of their understanding.

Their ability for their conciousness to enter into the physical realm is how they'd stand apart from the caelia.

The name demon is a bit misleading as it is a large category of entity from simple imps to incredible demi-gods. And not all ofnthem act with malcontent, some might act as guardian angels.