The Castellan restraints represent a method of brainwashing that the Intelligence Service of the Sith Empire utilized during the eras of the Cold War and the Galactic War. Potential candidates for Castellan conditioning were prepared through the use of IX serum, a substance derived from the chemical compound dimalium-6 found on the planet Quesh, and specially tailored to the individual. This serum required a period of three to thirty days to fully circulate within the subject's system, altering their brain chemistry to increase their susceptibility to suggestion; following the serum's complete absorption, a code word was imprinted on the subject, which, when spoken, would unlock their mind and compel them to follow any subsequent instructions. It was generally believed that this process was irreversible. However, archives from Imperial Intelligence revealed that the imprinting procedure could be repeated to reset the programming, although repeated administrations of IX serum were deemed "inhibiting".
Following Eradication Day, the Dark Council compelled the Keeper, who would soon become the Minister of Intelligence, to mandate the Castellan restraints for his promising agent, known as Cipher Nine. Despite Nine's success in defeating the rogue Dark Councilor Darth Jadus, the Dark Council considered an Imperial Agent's act of opposing a Sith Lord to be unacceptable; the alternative to the conditioning was the Agent's execution. Left with no other option, Keeper commanded Cipher Nine to undergo Castellan conditioning. The code word, "onomatophobia," was divulged by Hunter, a member of the Star Cabal, to Ardun Kothe, a former Jedi and the head of intelligence for the Galactic Republic's Strategic Information Service, for use in Cipher Nine's covert mission to infiltrate the SIS.