The Battle of Hogwarts was not won by the courage of the fighters. It was not won by their ferocity, nor their determination to protect. It was not even won by Harry Potter.
As the Death Eaters approached the school, a strange sound was heard. The clicking of claws, the rustling of grass, each all but silent alone - but together, it was amplified into a steadily growing, rumbling wall of sound.
And then they saw them.
Cats streamed from every window, every door, every hidden crevice in the walls. Even from the forest they came, ancestors long since abandoned, or escaped, or simply lost and never found. Hundreds, thousands, maybe even hundreds of thousands heeded the call. The tabbies and tortoiseshells, the bright whites and midnight blacks - the ground disappeared under a rippling ocean of fur.
Hogwarts was more than a school for children. It was a refuge, where the house elves always had a kind word and a spare saucer of milk, where a certain professor kept a secret supply of catnip in a hidden drawer (and could be persuaded to share, if one proved helpful), where a gruff old man would leap to the defence of any cat in seconds, doling out detentions left and right to students caught attacking them. It was a home.
The Death Eaters never stood a chance.
Some fell immediately, caught unawares. Some were able to draw their wands, but what use is a wand when you have no time to even cast a spell? What use is a spell when every opponent you fell is replaced by ten more? Screams rent the air as Voldemort's army was torn limb from limb, by tooth and claw and fury.
Of course, creatures cannot live in a place as steeped in magic as Hogwarts for any length of time without some of it taking root. Interestingly, many of the cats present that night could trace their lineage, if they were so inclined, back to the companions of the founders themselves. And there is very little that can surpass the deadliness of feline wrath. Not even the defences of a horcrux, held within a venomous snake.
Obviously, there were other soul vessels surviving. A battalion was dispatched to the Room of Hidden Things, tasked with destroying the corrupted diadem of Beloved Rowena, as she was once known, as soon as they were aware of it. It proved somewhat problematic - cats weren't designed to hunt metal, after all - but they prevailed.
And yet, on their way to report back to the Elders, they caught the scent of another soul fragment - of the same evil they had just destroyed. They followed it.
Harry Potter was very confused, not to mention frightened, to find himself assaulted by cats. He had been watching the bloodbath from a second-floor window, when suddenly he was on his back, covered in them. Tensing, he prepared to scream - but they weren't hurting him. They were... licking him?
AHH! His forehead burned! The cats were congregating there, licking and lightly clawing at his scar. It hurt! He tried to thrash but they were all over him. He couldn't move. He couldn't breathe. He couldn't-
The pain stopped.
A nebulous cloud of darkness hung over him, but even now it was dispersing. The cats withdrew, a few rubbing against him comfortingly, as silently as they had arrived. What in the world-?
Only later would he realise his connection to Voldemort had vanished at that moment, and all that that meant.
Mission accomplished, the cats reported their success to their leaders. Even the giants had begun to topple by this time; the werewolves were long since sent running, tails between their legs. Not that they made it far. The Death Eaters were annihilated. Only Voldemort himself was still standing, casting spell after spell to keep the hordes at bay.
But no-one can keep that up forever.
They gathered, readied themselves for one final charge. And what a charge it was! Many fell, but in the end, the outcome was inevitable.
All it took was one cat to get through. Her lamp-like eyes shined in the darkness, calculating and cold. She leapt onto the Dark Lord's back, sinking her claws deep into his flesh. Dust-coloured fur stained red, she once again tasted blood as she mauled his shoulder viciously.
The momentary lapse in Voldemort's defence, as he flung Mrs Norris back into the seething mass of feline fury with a curse and a flash of light, was more than enough.
The last image anyone saw of him still living was of him vanishing under a multitude of angry cats.
There was, in fact, a body, but only in the loosest sense of the word.
The cats dispersed as swiftly as they had assembled. They returned to their usual haunts, to lick their wounds and sleep away their aches. They took their dead with them - and over the next week or so, a few students found themselves lead to a hidden clearing in the forest, where flowers bloomed all year round (and if the feline population watched over them more closely than before, no-one spoke of it).
(If any staff were lead there, well, they never said a word.)
And that, my friends, is the true tale of the Battle of Hogwarts.