Isha

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

Pre-Fall history

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 (even though they are formed by the conciousnesses of the Eldar themselves, lulz). 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 (which pretty much sounds like an Eldar thing to do), 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.

During the Fall of the Eldar

Then the Fall of the Eldar happened, and things got real ugly. The only good thing to happen to Isha is that Isha survived Slaanesh's initial birth-slaughter, compared to other poor Eldar gods. However, Slaanesh, being what he/she/it is, decided to take Isha as his/her/it's eternal sex toy. Naturally, Isha started crying again, and someone again heard this time. However, it was the last person she would expect: The loveable bastard Nurgle had heard her cries and misery, like every other Chaos god, for a long time.

He however, decided to do something about it. He also realized he was feeling true, real love for another being. While the other Chaos gods kinda wished to give Slaanesh a little breathing room (He/She/It had just raped and killed most of the Eldar pantheon) until the birth subsided, Nurgle wasn't having that shit, so he challenged Slaanesh for the freedom of Isha, and won (thus setting a precedent for Him/Her/It vs the other gods).

Post-Fall status

To this day, Nurgle adores her like no one else can (well besides Kurnous being deader than dead). By the rules, she was his, and for a while, he would keep her in his Gardens and force-feed her many of his creations to see how long it would take her to succumb. Being a goddess of healing, she could cure herself, so if Nurgle was satisfied with the effects, he would release the contents somewhere in the universe - she could and still does take her time to whisper to the mortals as she has always done, to tell them how to cure themselves.

On /tg/

However, in /tg/ish canon, their relationship has progressed beyond what it was, and Isha can be said to love him back in kind. There is even debate whether she was chained in the Garden (where she could easily escape), or legitimately stayed behind. However, her reciprocation of love is always an uncomfortable one for Papa Nurgle, for he always worries that he's not good enough for her, and that she will leave him one day. She however, sees past his exterior for his true self, and his kind heart, and balks at the idea of leaving him.

Nurgle Daemonettes are a result of this.

In other /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.