Kassiyadin (Old Exekian, "the supernatural" or "the unseen") is the belief common in many Akhenist sects in a supernatural or spiritual realm beyond the physical plane of reality. This world includes the spirits of the unborn, angels, demons, and other such beings.

Some groups, such as the Vormundists, deny the existence of this realm altogether or attribute it to the unstable realm said to have been created by the mage Gwydion many thousands of years ago.

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