- "Oh! The Age of Aquarius, smothered in the crib! I am the triumph become dirge, the echo of the cheated dead."
Sigismilian is a ghost in the Immaterium, the sad remnant of an annihilated people. It haunts the impossible geometries of the idea-spaces outside the realms of Chaos, hiding from predators, and hoping to someday fulfill its purpose.
On the now Dead World of Chambrix, the mysterious Arahats gathered people of various races, rescued from battlefields and stranded spacecraft. These people became their students, practicing exotic forms of meditation and synchronizing their minds with the transcendent music of the Arahats. Over the course of thousands of years, a diverse collection of aliens became a cohesive civilization with a high propensity for Psyker births. Under the tutelage of the Arahats, the people of Chambrix developed such cohesive unity of purpose and thought during their mass meditations that they were able to create Sigismilian, an avatar of their collective will. Existing wholly within the Warp, Sigismilian's mere presence was anathema to the malicious entities it shared the dimension with, and was capable of completely obliterating them with a touch.
Understanding the potential threat of the Arahats and their students, especially if they should spread their ideology and methods beyond Chambrix, Tzeentch devoted a few fractions of a second initiating a plot to destroy them. Unwilling to risk exposing any of its own mortal agents to potential "corruption," an elaborate array of coincidences led to Douchard Bagge being led to Chambrix. Completely incapable of achieving enlightenment, and immune to any sense of fulfillment outside materialism, Bagge gassed the people of Chambrix to death in order to steal their vast trove of cultural treasures. Cut off from the collective consciousness of the Arahats and their students, Sigismilian was transformed from living epiphany to a shadow. Lacking in power and substance, it fled from the forces of Chaos.
Sigismilian is defined by its anguish. It is a sad and fearful thing that remembers that it once had in itself, an ideology for universal peace and brotherhood that was capable of bringing serenity to the Warp if only it could be spread far enough. Now it only has the memory that there was such a thing at one time, the specifics are completely lost. Sigismilian has literally forgotten more about life than most beings could ever learn. It is meek and fearful, fleeing at the first sign of peril but it desperately hopes to find some spiritually gifted, enlightened mortal (with psychic potential) to attach to.
Sigismilian was dreamed into being by a wide variety of species working in concert. It eschews any kind of classically humanoid appearance, and is instead expressed in the form of a chain of musical notation and molecular models of assorted neurotransmitters contained in a nimbus of rainbow colored light. When it interacted with others in the past, it would manifest tendrils of light to gesture and provide a frame of physical reference for those confused by its shape.
At one time, Sigismilian created a radius of "calmspace," in the Immaterium that repelled powerful entities and could obliterate lesser ones. The strength and size of this aura was dependent on the number of psykers trained in the Arahat method of rhythmic meditation. Now, it is simply able to navigate the Immaterium with great proficiency and communicate with those tapping into the Warp in some capacity.