Xelyth has pale blue skin that almost appears translucent in moonlight. Their eyes are entirely black, lacking iris or pupil, and they wear robes of deep midnight velvet that seem to drip water even in dry climates. Their hair consists of long, dark tendrils that sway as if they were underwater.

Xelyth is intensely curious and perpetually distracted, often appearing to listen to sounds that no one else can hear. They speak in soft, rhythmic whispers and frequently refer to themselves in the third person as if recounting a chronicle of their own life.

Xelyth was once a dedicated librarian in the undersea vaults of the Triton city of Melekar. While cataloging a shipment of wreckage from a ship that sank during a massive storm, they discovered a slate etched with impossible geometries. The moment their webbed fingers touched the stone, their mind was flooded with the visions of a slumbering entity deep beneath the crust of the ocean floor, an entity known as Thalassos the Unblinking. Xelyth realized that the Triton duty to guard the deep was far more literal than their kin believed, and that they had been chosen as a conduit for the void between the stars and the pressure of the abyss. This revelation forced them into exile from the libraries. They now wander the surface world, collecting knowledge for a patron that dreams in the dark. Their Tome is bound in the skin of a creature that has never seen the sun, and the ink inside shifts and moves when no one is looking directly at it.