Otherspace is another dimension beyond both realspace and hyperspace. While it appears to be a vast expanse of storm-gray nothingness, it does contain colored, swirling nebulae, and stars which are best described as "shining holes of darkness."
The Charon species are native to a planet within otherspace which is threatened by a nearby black hole. The presence of this interstellar disturbance caused an enormous amount of stress on the Charon's part and before long, the stress twisted their culture, giving rise to a death-worshiping religion. The members of this cult believe that it is their sacred duty to speed all life towards what they called the Void of Death.
After eradicating all of those who were unbelievers—which meant destroying all sentient life—on their homeworld, the Charon developed interstellar travel, and continued their holy mission. Eventually, all that remained in otherspace was a multitude of barren, lifeless planets. Biologically-engineered Charon starships still roam the void in search of any remaining traces of life.
In a multistage plan for his War of Darkness, Sivter had the Cult of Shadow develop the otherdrive, which allows ships to travel to and from otherspace. Once in otherspace, Sivter managed to convince the Charon that he was their mythical Prophet of the Void and began a process of outfitting all Charon ships with otherdrives in preparation for the war's endgame.