During the Reign of Blood, Goge Vandire wanted to make an example of the Imperial Sons, for... reasons (he's like that). He appoints a trusted Cardinal in command of some Brides of the Emperor, and sends them to Bastion. Upon meeting the Imperial Sons Commander, the Cardinal has a VERY BAD reaction, as the then Commander wields a C'tan phase sword, which (like all Necron weapons) repels the Warp's influence; this allows the Imperial Sons to expose him as a traitor (either a psyker, or a disguised Daemonhost). Ashamed they allowed a traitor to "pervert" their very reason for being, these future Sisters of Battle decide to fall upon their swords, but an Imperial Sons Chaplain convinces them to continue serving the Emperor in life; as a sign of trust, the Imperial Sons Commander gifts them the C'tan phase sword (the "phantasmal blade" that will become the Order's namesake).
Edited by Bjorn Firewalker, 21 December 2017 - 11:27 PM.