T'au.
How had Hades forgotten about them?
Perhaps because the other matters he dealt with every day were more urgent. Hades had been so busy his feet barely touched the ground that he rarely thought of this species—after all, the T'au were nowhere near enough of a threat to the Imperium.
Compared to Neos, the gambler who had staked everything; compared to Mortarion, leader of the heretics on another front; compared to Roboute Guilliman beside Hades, who constantly radiated, "I can tell you want to work overtime"—the T'au? They were simply too peripheral.
So peripheral that Hades never thought of them on his own.
But now, as he looked at the battle report handed over by the Raven Guard, Hades suddenly remembered this species that had been full of flaws in the original plot.
As a player in his previous life, and a devotee of the Plague God, Hades had not particularly liked the T'au, even when they had been absurdly strong in certain editions.
In short, one day, evil GW had slapped its forehead and decided to create a race that was kinder than the Imperium! More technologically advanced! More anti-dystopian! Friendlier to other species! More seemingly full of hope! And equipped with a whole pile of mechs that did not look like they belonged in Warhammer at all!
And so these blue-skinned fish-men appeared.
Incidentally, when GW created this species, it had also stitched together plenty of existing Earth cultures. Just as the White Scars were Space Mongols, these blue-skinned T'au carried an intensely East Asian cultural flavor—especially Japanese.
If that had been all, Hades would not have frowned at the species. The problem was that in the subsequent T'au stories—guess who kept getting used as a stepping stone for the T'au?
That's right! The Imperium of Man!