Isha

One of the many Eldar gods, Isha's domain is healing, fertility, and the harvest. She is one of the few genuinely nice Warp-entities in Warhammer 40,000.

So, naturally, grimdark things happen to her. A lot. To give some sense of scale, the story behind Eldar's spirit-stones is that they are Isha's tears. Seeing as there were once trillions of Eldar, and enough spirit-stones for all of them, Isha has been crying quite a bit.

Long ago, before the Eldar got into their hedonistic shit, Khaine learned of a prophecy that an Eldar would kill him, so he did the only rational thing in this universe: start wiping out the Eldar. Isha complained to Asuryan, King of the Eldar Gods, to stop this. At first, Asuryan's response was "cry me a river". You can imagine his surprise when she did just that in his palace. Not wanting to ruin his floors any further, Asuryan told Khaine to calm the fuck down, and ordered the Gods to cease interacting with the Eldar. Isha had a bit of a problem with this, and so met the Eldar in secret. When Khaine found out, he imprisoned Isha and her husband Kurnous. The other Gods thought this was kind of extreme, but only Vaul, the Smith God, did anything about it, offering to make one hundred swords to pay their ransom. Since Vaul's swords were really fucking powerful, Khaine agreed to release them in a year. Problem was, Vaul only made 99 in that time, so he threw in a regular sword. Isha and Kurnous were freed, but when Khaine found out, he imprisoned Vaul instead.

Then the Fall of the Eldar happened, and things got real ugly. The only good thing to happen to Isha is that, when Slaanesh was born, Nurgle protected Isha from getting eaten like the other Eldar gods; apparently, he was smitten with her. He shows his love by force-feeding her his new diseases, sending the ones which cause the most interesting reactions out into the galaxy. Isha makes the most of her predicament by healing herself, and whispering the cure to the galaxy.

In /tg/ canon, the Emperasque recently rescued her from Nurgle's garden; he claims he only did it because he needed leverage over the Eldar, but he's also apparently a much nicer guy after ten thousand years of forced introspection.