Sounds promising. This is from the 40 Wiki:
Slaanesh & Eldar:
The birth of Slaanesh marked the downfall of the Eldar, who refer to Slaanesh as She or She Who Thirsts referring to Slannesh's constant hunger for their souls. Their home worlds were destroyed by the shock wave, along with many of the craft-worlds created by the most forward seeing among them to escape the disaster. But the destruction of their homes and the death of their brethren was not the only disaster for the Eldar. Slaanesh proceeded to combat the very gods of the Eldar, slaying all but three: Khaine, Cegorach, and Isha, who is held captive in the garden of Nurgle.
Born by the very essence of Eldar being, Slaanesh has fed on the race ever since. When most Eldar die, if no soulstone is present to receive their soul, it is consumed by Slaanesh. The Eldar have taken many steps to defend themselves against the attacks of Slaanesh, including a strict code of "paths" or ways of studying a particular aspect of life or occupation to avoid unbridled seeking of pleasure or knowledge, and Soulstones that shield the souls of the fallen against the predations of Slaanesh.
The enigmatic group of Eldar known as the Harlequins go through what is known only as "The Ritual" to free themselves from this fate, and it is believed they are then under the protection of Cegorach or "The Laughing God" or "The Great Harlequin" (also a title used for a high ranking leader of the Harlequins). The even rarer beings known as the Solitaire, who are alone in their ability to play Slaanesh in Harlequins most rare of dances, is said to already belong to Slaanesh, is considered cursed, although it is also said that when a Solitaire dies, Cegorach will emerge from the Webway to fight Slaanesh for his soul.
The sadistic Dark Eldar do not protect themselves against Slaanesh, and their souls are devoured even as they live. Unlike the Craftworld Eldar, they continued the acts which brought about the creation of Slaanesh. To slow the drain of their souls, they drink the souls of others, prolonging their lives.
