Codex: Chaos Daemons (2008), p82 — The Caged Maiden

The Eldar believe that their gods are dead, destroyed by Slaanesh when the Dark Prince awoke. Yet there is one myth upon a single craftworld that tells of how the maiden goddess Isha was not slain by the Prince of Pleasure. Instead, when Slaanesh claimed Isha as his own, Nurgle heard her cries for help and her anguish touched his leprous heart.

Isha was a goddess of fertility and healing, the embodiment of life, and mighty Nurgle wished for her to become his companion. Nurgle waged a long war against Slaanesh to wrest Isha from the Dark Prince's grasp and was eventually victorious.

Yet the adoration of a Chaos God is a strange thing, for Nurgle shows his affection in cruel ways. Nurgle keeps Isha within a rusted cage in the corner of his cauldron chamber. When the Plague God creates a particularly pleasing brew, he forces Isha to imbibe the putrid mixture, watching with building excitement for the symptoms of his latest contagion.

Though Isha can cure herself of the disease's ravages, the speed with which she is freed from its grip allows the Plaguelord to evaluate his creation's virulence. If Nurgle is pleased, he returns to his cauldron and empties its contents into a bottomless drain, the noxious liquid falling as rain upon one of the mortal worlds. If the concoction does not meet with Nurgle's approval, he gulps down the contents of the cauldron, vomits it back into the pot, and starts afresh. While the Plaguefather is busy at his cauldron, Isha whispers to mortals, seeking to tell them the cures for the poxes she has tasted.