In the mirror universe, the Kaylar were originally native to Rigel VII, but eventually became a slave race within the Terran Empire.

It was in 2254 that a fight broke out between crew members of the ISS Enterprise under the command of Captain Christopher Pike and a group of Kaylar warriors. In response, Pike bombarded the surface of Rigel VII, destroying many Kaylar camps and religious sites. In the following years, the Empire's slave traders arrived on Rigel VII and exported 90% of the Kaylar population.

Over time, Kaylar slaves became fashionable among the Empire's Terran aristocracy, as they were reminiscent of some of Earth's earlier remote populations. Kaylar men were often used as ceremonial guards, whereas Kaylar women served as pleasure slaves.

A small population of Kaylar remained on Rigel VII, hidden deep within its forests. (Decipher RPG module: Through a Glass, Darkly)