... and so it was in this bygone age that the Trimurti stood together on a hilltop overlooking the battlefield, their proxies and attendants waiting nearby. Below them, Arvandor was burning - the tanar'ri army had won the day once more. Led by the fallen asura prince Mahish, they seemed unstoppable. The demonic host was cutting a path into the upper planes, slowly approaching Mount Meru, the seat of power of the Hindu pantheon.
The Trimurti observed for a time before the Lord Destroyer addressed his peers.
"Verily, we are boned."
"Oh, do shut up, Shiva" replied the Lord Preserver. "This is all your fault anyway."
"My fault? How exactly is it my fault if Brahma's idea of amusement is bestowing the power of invulnerability on his asura pet?"
"Well, you were the one that voted against sending reinforcements to Indra when Mahishasura got out of hand and started gating demons into Limbo. We could've stopped them at Swarga, and instead..." the Lord Preserver gestured toward the battlefield below.
"Indra's an asshole, anyway" said Shiva, waving his mighty trident dismissively "and stopping them back in Limbo wouldn't have been any easier than stopping them here. Why don't you go ask Creator boy over there how he's going to deal with his invulnerable asura?"
The third of the Trimurti kept his silence, sitting calmly upon the back of the Garuda bird. Shiva and Vishnu kept on bickering, and once the Brahma had heard enough, he raised his hand. The other two fell silent and turned respectfully to hear what Brahma had to say (for although technically equals of the Lord Creator, the lords of Preservation and Destruction possessed lesser personal power in those days, when the planes were still young)
"Even the Trimurti make mistakes, and today we have to face the consequences of one." said the Lord Creator gravely.
"I can't undo the gift of invulnerability that I gave to Mahish, because it is not in my power to undo anything. And no, you can't undo it either Shiva, because the time when your gift will be able to overpower one of mine is still far. Still ... perhaps together we can create something that will undo both the invulnerability and the rebel asura scum as well. If, that is, you are willing to sacrifice of yourself."
"Of myself? You mean give up a part of my essence so that you can forge some... weapon out of it?" asked Lord Destroyer, disbelief obvious in his voice.
"I don't like it any more than you do, and it might turn out to be a new mistake, the consequences of which I cannot even begin to predict. Still, if we do not act now, I'm afraid even the Great Wheel itself could eventually be stopped. And where would that leave our retirement plans?"
Gasps were generally issued, as the other deities thought of their precious retirement plans, those small and tastefully decorated demiplanes to which they would retreat after the cycle had completed... Eventually, Vishnu's laughter broke the stunned silence.
"Wait, you two give up some of your strength to unite forces? Sounds great to me, except whatever it is you build will never hold."
"That's where you come in, sibling. You'll also have to sacrifice of yourself to make our creation permanent. Besides, did you think we would willingly diminish ourselves and leave you dominant? Really, little brother. Think of the balance issues for once, would you?"
"Oh. Weak." said Vishnu, and Shiva just snickered.
And thus had the Trimurti joined their powers for the first and last time. Brahma took earth, blood, and iron from the battlefield, and shaped it into a humanoid form with many limbs. In his wisdom, he made it into a female, so that they could easily pour their divine essence into the creature.
Brahma stepped forward, opening his crown chakra, and spoke: "I name you Durga, and Shakti, and Devi. I name you Strength, goddess. Rise."
Next was Vishnu, who gave from his heart chakra, and sang to the stirring entity: "I name you Parvati, and Uma. I name you Light, goddess. Rise."
Finally, Shiva approached and opened his sacral chakra, whispering to her: "I name you Kali. I name you Murder, goddess. Rise."
And so she did.
The goddess of many names opened her eyes, and blades of iron extended from her body. She stood, and her beauty was so great that all creatures averted their eyes, except a proxy called Krishna, who came closer and said "Well, hello therrraaaargh!"
She saddled a lion, and rode singing toward the screaming tanar'ri horde.
Much later, after the demons had been routed, the fires put out, and the head of Mahishasura presented to the Trimurti, the newborn Power left to create her own realm. Shiva suggested she could always crash at the Vortex if she liked, but that initiative went down like a led balloon.
All the gods of the pantheon were quite impressed by the new member; even the usually jealous goddesses were intrigued by the idea of a universal female power present in them all, and the seeds of several warrior-mother cults were planted that day.
The few sad remains of mortal armies that had been thrown at the demons as cannon fodder huddled together, uncertain how, when, or if they would get back home. The particularly vicious among them were retelling the unknown goddess's ferocity and battle prowess. The first statuettes were being carved from wood and stone. Strangling cords were being sanctified. Even though millennia would pass before Durga evolved from her warrior aspect and toward the murdering whore that rules the Caverns of Skulls today, the mortals sensed that the Age of Iron would eventually come.
The song of Kali had begun.