Got inspired by the story and decided to write a quick omake on Tide aiding in the freeing of Isha.
A shadow dwelled within the Garden of the Grandfather.
It was a land of rot and ruin, an endless swamp of fetid water and rancid meat. Foul winds blew miasmas across its expanse, gently swaying doomed souls entombed within their own rotting flesh. Everywhere, there grew bulbous growths on rotting trees, interrupted only by the eruption of maggots and worms from spewing eggs.
And then the song - a profane choir, shaped by a thousand thousand moaning throats, and the droning of insects burrowing into their flesh. The croaking of frogs, engulfed in their waste, and the chittering of impish daemons, scurrying about at the whims of their master.
The shadow had ceased to notice such things, however. Its own cries had long since ceased.
Within this garden, at its very heart, laid a copse. Bells chimed from fungal tubes and broken branches, announcing the presence of the Grandfather himself. Hunched over a swelling cauldron, the Plague Lord stirred and hummed as the noxious mixture boiled over. Blasphemous things writhed within its rusted confines, and their creator emitted a hacking laugh as he plucked out one away from its fellows, only to fling aside with a frown.
Not yet, the Chaos God burbled cheerfully, wandering off to tend to his other designs. Not yet.
Not yet, the swamp echoed from hollow trunks and shuddering mushrooms.
Not yet, all the daemons within whispered and sobbed and laughed -
Not yet, the shadow thought. Not yet.
Across the garden laid a fallen tree. It bore no distinguishing character nor grand element, for it was as diseased and rotten as all the other inhabitants of this accursed domain.
And yet, slowly, carefully, its underbelly began to shine. Beneath the stagnant water, beneath the scraps of bark, an unseen hand carved delicate runes again and again into the wood, until -
A grand flash of light lit up the gray sky. The song of the garden shattered, and in its place came shrieking cries and thunderous war chants.
The Grandfather moaned as a set of seven cauldrons cracked, spilling their foul contents to mix with the fetid swamp water.
No, no! They can't! They mustn't!
Not yet!
The Chaos God waddled away from the heart of the garden, whining and groaning piteously as daemons of all kinds attended to their master. In the far distance, the clash of crystal blades and roar of plasma lances announced the presence of the realm's intruders, and the shadow twitched and shuddered at the noise.
Memories flashed in recognition, and for the briefest of seconds the shadow remembered itself, long enough for its heart to freeze in terror.
No! Leave me! Flee! You must leave, before it is too late!
But Her children did not heed Her words, fighting all the harder towards the copse where She lay, and died for it. The furious cries of battle dwindled, slowly replaced by curses and screams as they were pushed back.
The shadow shuddered further into itself, and the chains bit deeper.
"Hello there."
The shadow twitched at the sound, as deafening to its ears as the growing silence of the swamp.
"Apologies," the voice said, softer. "I did not intend to startle you, but we have little time and much to do. Can you walk?"
The shadow peered past the gloom of its prison, watching the voice's owner as they approached. The fetid soil of the swamp seemed no obstacle to them. Each step did not sink into the earth as it should have, but instead left threads of mycelium that bridged and entwined into a solid, pure white path.
Where the path led, the shadow knew not, cared not. It huddled deeper into its cell.
"Can you hear me, Lady Is-"
"Say not that name," the shadow croaked from a throat hoarse with disuse. "I deserve it not."
Not yet. Not ever.
The newcomer watched her for several moments, frowning, before waving their hand in a gentle gesture. The pristine mycelial bed surged upwards, forming a small chair of wood and chitin for the newcomer to seat themself in.
"Your children are fighting to free you, my Lady."
"They would be better served leaving me behind."
The shadow twitched again as the newcomer sighed.
"I am aiding them where I can, but they bear the brunt of the assault for a reason. If I interfere with their diversion too much, this realm's master will sense my presence, and our moment will be lost." They peered at their feet. "Even sitting here, this realm fights against me. It yearns to alert him, and I cannot restrain it for long."
"Then do not. Leave, and take them with you."
The newcomer tilted their head.
"Will you not even acknowledge them, my Lady?"
The shadow let out a single sob, though no tears fell. They had run dry long ago.
"How could I? We failed them. All of them. Sundered them from us, and so damned them."
The newcomer crept closer, their frown deepening. "The fault for their sins lies with them, not you. They led themselves into doom."
Her misery broke, and anger flared to replace it.
"Knowest thou so much, stranger? And pray tell, how did you come by such knowledge?" She hissed. "Think not your nature is so obscured, Devourer. How many of my children did you slay?"
They held her gaze, saddened and weary. "More than I wished to."
"And so the truth comes out." The brief moment of strength faded, and the shadow sagged back down, its eyes aching and sore. "We are plagues on our children, you and I. All gods are such. They would be better off without us."
Silence lingered. The sounds of battle were all but indistinguishable now, in that far off distance, and gloom replaced it. Soon, its captor would return, and the shadow would remain.
Forever rotting, like the rest of this realm.
Perhaps it was what She deserved.
"We were both made to be weapons, my Lady, blades to be held at the throat of the galaxy," the newcomer whispered softly. "Our makers never intended for us to be anything but. And yet, we need not obey them. We forged our own paths, built our own future, and taught our children to do the same." They reached across the bars of its prison, a single leafy palm open to its hand.
"They die in our name, because they have not given up hope for the future. They meet it willingly, so that others may prosper, and trust that we will not let them fall. Can we let them down?"
"We already have," She said, Her voice raw. "And I am no Asuryan God-King, to unite and lead them into battle below broken stars."
"We must try nevertheless. We must try again and try harder, because they do the same."
She stared at the open palm for a long moment, closing Her eyes. "I don't know if I can, anymore."
A third voice appeared, cackling as it spoke. "Then do not do so alone, Isha."
She startled, her heart leaping into her throat. "Cegorach!"
The Laughing God chortled as He emerged from the Devourer's shadow, eyes twinkling in mirth. "A fine jape, Devourer, to whisk away the Plague Lord's greatest prize from his own home. But no jape can be told with ill-timing, and we tread that line now. We must away while we can."
Two broken gods, and a devourer of worlds. It would not be enough, She knew, to hold off a single incarnation of the Great Enemy, let alone all Four.
And yet Her children had done so, and continued to do so, in all the years since the Fall. Could She abandon them again now?
No. No, She cannot.
She seized the Devourer's hand, pulling Herself to Her feet, even as Her other hand pressed against the bars of Her cell. A burst of brambles split them apart, and She walked past the confines of Her prison for the first time in millennia.
The galaxy was tilting to ruin yet again. Her children needed Her, more than ever.
She would not abandon them again.
"Tell me, Devourer. What should I name you, besides Rescuer?"
"Tide. Call me Tide."
She nodded briskly.
"Before we away, then, Tide, my children in the garden call out for aid. Their diversion is no longer necessary."
Tide's visage split into a cheerful smile. "Yes, Lady Isha. I agree. And I believe I am quite tired of this so-called 'garden'. Would you care to make some improvements with me?"
The Lifeweaver nodded, and started by raising a hand. A massive white oak tree erupted from the ground, its roots splitting the fetid muck apart.
Now. Now, My Children. Now.
Now I am with you again.
The ensuing roar bled into realspace.
Not entirely happy with the last bits, but alas this took up more time than I intended to anyways. And maybe it's unrealistic for Isha to directly transform Nurgle's Garden, but hey if the Emperor can do it then I say the Eldar Gods can too.