Sethis is a maligned system of little obvious merit. Composed of the frozen world of Sethis Major and its moons Sethis Minor, Deredeum, and Lirithene, the system was, for the majority of its known existence, one of the Macharian Sector’s least promising prospects. However, since its colonisation, a few members of the Adeptus Mechanicus have attempted to reconstruct the system’s desultory past, the better to chart its future.
Sethis lies near the shrine world and sector capital of Macharia, yet it is cruelly separated from this seat of faith by the Azynith Abyss. A stretch of uncharted, warp-riddled space, the Abyss’s relation to material and immaterial reality has not been well documented, or at least such documentation has not been published.
For untold millennia, the Sethis System turned in the void unwitnessed and unclaimed. What little is known of this period comes from fragmentary geologis surveys which suggest that Sethis Major was not always frozen. Ancient strata hint at oceans, atmospheres, and perhaps even life, though whether this was xenos contamination or some earlier human settlement is a matter the Ordo Xenos has shown occasional interest in and the Adeptus Mechanicus has shown occasional interest in suppressing.
What is certain is that by the time mankind returned to the stars, Sethis was already cold, sunless, and profoundly hostile to human life.
Records of Sethis in the Administrarum’s vaults on Macharia indicate that the system was first catalogued in 901.M34 However, the system was not claimed until the year 444.M41 when the rogue trader Lenryk Leeran made a fly-by aboard the Luneste, establishing that the system's major planet was "frozen, sunless, barren, and inhospitable", and its moons "various in character, uniform in antagonism to human life".
Beyond the system's sparse bounty of natural resources, it was further vilified for its proximity to the Rictus Borealis, a crimson warp rift that sits like a long, bloody wound in realspace, threatening untold hell. It was for this reason that the Adeptus Ministorum proscribed the settlement of the Sethis System and a note was hastily added to its entry in the scrolls of the Administratum: "Death World".
For two Terran centuries, the Leeran dynasty maintained its claim as little more than a formality—a line on a charter, a name on a map, and the occasional surveyor expedition that returned with frostbite and little else. The system became a punchline among rogue traders: "Leeran's Folly," they called it, another frozen corner of space where ambition and solars went to die.
The dynasty of Leeran continued to claim the system as a hereditary fief, a claim that bore fruit when it was discovered that vast volcanic pools were bubbling at a shallow depth below Sethis Major's north pole. This proved to be the planet's salvation as the Adeptus Mechanicus were quickly charged with mining this energy and using it to kick start the system's rapid industrialisation and development into a serviceable spaceport and fortification against possible incursions from the Rictus Borealis.
In the ensuing frenzy of claims, the voice of House Leeran sounded above the rest and they were given control of the system in line with their historic claim. It was a remarkable coup: from laughingstock to planetary governor in the span of a single generation. Naturally, competing dynasties contested the legitimacy of Leeran's authority, and for several decades the system was host to bitter politicking, assassinations, and at least one small-scale naval skirmish that left wreckage still orbiting Sethis Minor.
The Tech-Priests of Mars, for their part, cared little for dynastic squabbles. They set to work immediately, sinking vast thermal shafts into the planetary crust and erecting the first manufactorums within what would become Hive Omin.