Slaanesh was so free-spirited and undisciplined that she naturally paid Khorne's warning no mind, even mocking him with considerable disdain.
"Who the hell are you?"
That single sentence successfully ignited Khorne's rage. From then on, besides Tzeentch—that stinking pile of dog shit he loathed—Slaanesh, that disrespectful and utterly disorderly creature, joined the list of people he regularly beat up.
Even though time and space had no meaning within the Warp, and every god existed in both the future and the past, that did not stop the Blood God from pinning newborn Slaanesh down and delivering a savage beating while roaring at the top of his lungs about who the true big brother was.
The Blood God's apocalyptic weapons collided violently with Slaanesh's bizarre indulgence toys, accidentally smashing Cain to pieces as well.
From then on, this madman who had given the other Aeldari gods such headaches was scattered everywhere. Only the C'tan shattered by the Necrontyr could compare to him in terms of fragmentation.
The collapsing Aeldari Empire suffered the agony of Slaanesh devouring its souls, the catastrophe of its pantheon's fall, and the deep corruption of Cain's fragments.
Cain's fury assailed the Aeldari's souls and minds, causing bloodlust and tragedies of mutual slaughter to unfold one after another.
Even the Craftworlds that escaped the heart of the Aeldari Empire could not escape this madness. They burned amid civil war, and driven by the mad Shattered God, the surviving Aeldari entered another great battle royale.
Only when the Phoenix Lords brought the Path system could the Aeldari control their own actions.
Yet that control was ultimately only the most basic safeguard. The Aeldari still risked turning into bloodthirsty madmen.
Thus, the war mask was born. It was not equipment, but a method of splitting one's war mentality from one's everyday