The Rilzak is a small, resilient fish species native to the geothermally heated shorelines of the Dark Sea Region, particularly near the Ralar Volcano, where volcanic activity creates an unusual warm-water microclimate. Adapted to both the extreme cold of the Dark Sea and the mineral-rich heated vents along the coast, the Rilzak has developed unique physiological traits that allow it to thrive in an otherwise inhospitable environment.

It plays a crucial role in the local food chain, serving as both prey for larger predators like the Sulak and Shadul and a scavenger that helps regulate the balance of the volcanic ecosystem.