This short story was originally published in Facebook Group, "The Imperium of Man", last year. Seeing that BFG Armada 2 is up and stories being told here, I think it would be a good time to publish segments of my crossover story here.
The vast cosmic construct lay hanging in the endless night of the void. Dead. Cleaved in twain. A mighty weapon no more.
Spire was impressed by these humans' capability in constructing something wondrous and immense as this machine. Even the Mechanicus would drool over this miracle of a technology. Its FTL needs no Warp to traverse the Galaxy, save for accurate maps and even more accurate cogitator calculations. It could house dozens of regiments, store years' worth of supplies and tend to fleets alone. The construct had a massive potential in changing the outcomes of the Imperium's many deadlocked campaigns.
*Why? Why for this purpose so trivial that this great construct is used for?, lamented Spire in his mind. Such a worthy opponent, spent on a useless task.
Captured enemies claimed that it was made to keep its subjects in line. To make known the strength of their "Empire". It destroyed planets to make a point.
What a waste, mused Spire.
Mechanicus savants estimated that for this machine's scale, it would bankrupt its entire government and starve whole system populations just to manufacture it. Moreover, the fact that the Tech Priests analysed that these humans can eradicate planets through their ships' conventional bombardment, just like the Navy's own way of Exterminatus, just adds up to the wasteful inefficiency this "Empire" made in crafting this weapon.
Spire frowned, not even the Munitorum could squander resources as mindlessly as this.
There never was a showdown between this construct and his Retribution-class Flagship Bloodhawk. Spire hoped it would be like duelling The Blackstone Fortresses or even Abaddon's own Planet Killer. Subsequent scans exposed a large Achilles' Heel on one of its sides. A single bombing run of Starhawks supported by Furies to ward off their miniscule fighters was enough for the task.
Spire's disappointed eyes fixed itself on this ruined device. They gave it a curiously intimidating name that sounded more like a propaganda tool than an actual military asset.
The Death Star.