The T'au possessed technological wonders that even the Adeptus Mechanicus might begrudgingly admire, but among their most curious assets were the biological starships of their allies, the Kroot.
The Kroot are an avian-derived species. While they appear primitive at first glance, their biological engineering is sophisticated in its own unique way. They live as nomadic mercenaries, yet they traverse the stars in "Warspheres"—colossal, spherical fortresses that serve as both transport and hunting grounds.
Yes, hunting. The Kroot are apex predators who consume their prey raw. Their physiology is remarkable: they possess sensory quills, dense musculature, and digestive systems capable of breaking down almost anything except adamantium. By consuming specific prey, the Kroot can filter and incorporate the genetic traits of those creatures into their own DNA over generations.
This was exactly why the Overmind had directed the Swarm toward T'au space. Some might think, "Why pick on the T'au? They're just a tiny island in a galactic ocean. Go fight the Imperium!" But anyone seeing the Kroot's racial traits would realize the Overmind's genius. The Kroot are essentially a "lite" version of the Primal Zerg. Much like the denizens of Zerus, they evolve by devouring. While they aren't as efficient as the Swarm—they wouldn't dare eat a Tyranid, for instance, for fear of being subverted—they are still a goldmine of adaptive genetic material. They even eat Orks, though doing so carries the risk of growing fungal spores on one's own head.
"Zasz," the Overmind commanded, "don't just focus on the boarding actions. Send out Overlords and Eyeworms to scout the neighboring systems. Actively hunt for the Kroot."
"As you will, Master," Zasz replied.
Dozens of Eyeworms were launched into the void. Within ten days, they reached nearby star systems, exploring planets so harsh that even the Zerg found them unappealing. However, the scouts eventually bore fruit.
The T'au in these neighboring systems were blissfully unaware of the invasion. Merchant ships laden with cargo sailed from orbital starports, following well-traveled trade lanes. It was near one of these system's moons that an Eyeworm spotted a perfectly shaped, dormant sphere: a Kroot Warsphere.
"Found it."
The Overmind couldn't strike immediately. While T'au FTL is slow, their localized industrial output is staggering. If he moved too soon with a small force, Zasz's splinter fleet could be overwhelmed by sheer numbers. The main Zerg Hive Fleet was still locked in a death match with the Tyranids of Tiamat and could offer no reinforcements. Zasz would have to win this with what he had.
"Eyeworm, deploy the Changelings. Let's see what they're hiding," the Overmind ordered.
The Eyeworm slipped into the atmosphere of a T'au colony. Far from the pristine cities, it birthed several Changelings—pitch-black, amorphous blobs that wriggled and shifted until they took the form of T'au Fire Caste warriors.
"Infiltrate their society. Be my eyes and ears."
However, the Overmind underestimated the cohesion of T'au society. Unlike the sprawling, indifferent hives of the Imperium, the T'au looked out for one another. Within minutes of a Changeling entering a city, a Kroot mercenary and his pack of Kroot Hounds began to trail it.
Even the Overmind didn't realize what was wrong at first. The mimicry was visually perfect, even replicating the texture of the pulse armor. But a Changeling's "armor" is soft to the touch, and more importantly, it lacks a biological scent.
As the Kroot and its Hounds closed in, a squad of Fire Caste warriors suddenly intercepted the Changeling, pinning it to the ground. Under the physical pressure, the creature's form destabilized, melting back into a purple-black mass of protoplasm.
"By the Ethereals, what is this monstrosity?!"
"I told you he smelled wrong," the Kroot grunted, his beak clicking in disapproval. "He had no scent of the sept. Now you believe me."
"Hold it down! Watch the—agh, it has claws!"
The Changeling lashed out with the same serrated talons used by Infested humans, piercing a warrior's armor. Before it could do more damage, the Kroot Hounds pounced, tearing the mimic to bloody shreds.
The psychic link severed. The Overmind fell silent for a moment.
"Well, damn."
The Changelings could mimic sight and sound, but they couldn't fool the predatory nose of a Kroot. "Note to self: scent-masking is the next priority for Abathur."
He decided to pivot. If infiltration failed, he would simply stockpile a fleet and take the world by force. But as he reviewed the data from other Eyeworms, he found a bizarre anomaly on a distant planet at the edge of the T'au's reach.
The planet's surface was covered in a thick, weeping fungal forest that exhaled decaying spores—a twisted landscape of rot and unnatural vitality. T'au are usually very picky about their environments; they wouldn't colonize a swamp of filth.
As the Eyeworm hovered over the city square, the Overmind's many eyes widened. In the center of the plaza stood a massive, bloated statue of a Great Unclean One.
"Are those... Nurgle-corrupted T'au?!" He had always heard that T'au souls were too "dim" in the Warp to interest demons. If the Plague God had managed to claim them, the galaxy was in even worse shape than he thought.