The woe of the Aeldari, the Chaos God Slaanesh, desired the jewel known as Kher-Ys, an Asuryani Craftworld rich in souls and drifting dangerously close to the Eye of Terror. The covetous Dark Prince and his minions gathered in a great host to seize their share of the prize, but Kher-Ys was extremely well protected. Wards of energy sealed the Craftworld from the Webway, and Aeldari warriors patrolled the Silver River that led to her gates.
With siren calls to the Aeldari within, the daemons of Slaanesh assembled around the Craftworld, attempting to enchant those within with their sibilant voices of desire. For the most part, they were ignored, but a few were lured from the sanctuary of their Craftworld with the whispers of promised decadent adventure.
One particular innocent Aeldari girl attracted the attention of the Heartslayer. Her innocent soul blazed brightly within the Warp, but at its heart lay a dark shadow. This flickering enigma attracted the attention of the Heartslayer, who resolved that within the girl's spirit lay the key to taking Kher-Ys.
Clad in the guise of an Aeldari male, the Keeper of Secrets travelled the Silver River and bewitched the maiden with its glamour and guile. She fell under the Heartslayer's spell and was soon convinced to return with him to her home. Swathed in the love that only one Aeldari could give to another, Heartslayer was able to penetrate the impassible barriers of Kher-Ys, and stole within.
Seeking the means to open the great portal that led to the Silver River, Heartslayer discovered it was held fast by a psychic key -- one, he soon found, held by the maiden's father. As the Aeldari male slumbered, the foul Greater Daemon ripped it from about his neck, then used it to open the wards upon the Webway, allowing Slaanesh's vicious daemonic horde to descend upon the unsuspecting Craftworld.
Heartslayer finally revealed his true form, his terrifying visage towering over the frightened Aeldari. Drawn to the heart of Kher-Ys, the Greater Daemon made his way towards the chamber where an Avatar of Khaine, the incarnation of Kher-Ys' warrior spirit, still slumbered. The Heartslayer gloated over its dormant form, inert and helpless. Then some spark awoke the Avatar's spirit, rousing it from its slumber. Blazing into life, it seized the Heartslayer and attempted to strangle the Greater Daemon in its unbreakable grip.
But since the Avatar had not been awoken and tamed properly with the sacrifice of the soul of an Aeldari High King, the soulless thing remained a hollow construct. Seizing an opportunity, the Heartslayer was able to invest himself into the shell of the Avatar, perverting it from within.
The Keeper of Secrets, in the borrowed form of the Avatar of Khaine, led the Slaaneshi Daemonhost in an orgy of destruction. They gorged themselves upon the Aeldari souls of Kher-Ys for many solar days and nights as thousands fell to their insatiable thirsts. Slaanesh finally claimed his prized jewel.
The empty and desolate Craftworld of Kher-Ys continues to drift along the eddies of the Eye of Terror, its corridors still ringing with the psychic echoes of the death cries of its people and the laughter of their daemonic slayers.
- Codex: Daemons (4th Edition), pg. 26