The Marasa Nebula was a chaotic cloud of highly energized gas which blocked hyperspace travel along the Trellen Trade Route. Since travel through the nebula was too hazardous to consider, starships traveling the route were forced to take a wide detour around the nebula during the days of the Galactic Republic.
The Galactic Empire's probe droids investigated the region, searching for mineral resources and a possible safe shortcut. The Empire was surprised to discover the Marasans, an advanced civilization which had developed in isolation within the nebula. The Marasans, who had interfaced navigation computers with their brains as cyborg implants, could chart routes to all thirteen systems in the nebula by finding anchorpoints which allowed them to travel safely. By the time the Empire made contact, the Marasans had spread from their homeworld, Marasai, to set up over twenty colonies in the nebula.
Unable to duplicate the Marasans' methods, the Empire elected to conquer the cyborg aliens, forcing them to guide their starships through the nebula.
The Marasa Nebula was also inhabited by giant plasma-fliers, large creatures which hid within the nebula. Marasan starships were armed in order to fight them off.