A world kind of on the fringe of the Known Multiverse it inhabits its own pocket dimension that’s protected from outside intrusion, and the only way in and out is through a special magical portal called the Screaming Wall, which was created thousands of years ago by Dhal of the dour, who founded this place after carving it out of the orbit of one of the Hell Worlds.
Here the dominant forms of life are Dragons and Demons and humans offer themselves up as sacrifice to both of them without the slightest hesitation because in doing so they know that they get automatic resurrection for dutiful and faithful service. Not only that but they’ve even developed Cloning technology that allows them to make perfectly gene-sculpted bodies that they can grow in less than a day or so. That means they can have an empty vessel on hand that they keep in a preservative chamber that is without a soul right up to the moment when their consciousness is transferred by a special jeweled crystal called a Soul Pearl. They have a giant Matrix Stone in the Palace of Uxal that relays souls from bodies that get terminated to fresh bodies that are waiting for occupancy. So most folks in the civilized corners of Uxal keep at least a couple of spare bodies lying around just for emergencies with other places mass-producing clone bodies for industrial strength usage, which is one better than the scientists of my world have ever been able to come up with.
Siren learned it from one of her own descendants, an Archmage by the name of Marinlae Starsong, who was its actual creator.