There were many in this world who feared and loathed Grindelwald, but precious few who dared to truly hate him. Of those few, none hated Grindelwald more absolutely, more completely, than Aberforth Dumbledore.
The thunderous declarations Grindelwald had bellowed moments ago had echoed through the castle walls, and with only a single mountain between them, the village of Hogsmeade had heard every word just as clearly.
The reason Aberforth had arrived later than expected was simple: the surrounding space had been churned into utter chaos by the clashing magical forces, and when he attempted to Apparate, he failed for the first time in his life, overshooting his destination by a full twenty miles.
"Grindelwald, I want you dead!"
A goat Patronus blazing with brilliant blue light came charging ferociously toward Grindelwald. From where Tom stood watching, Aberforth astride a broomstick crashing headlong into the battlefield looked, in no small measure, like a rougher, angrier version of his older brother.
"Aberforth?" Grindelwald deflected one of Dumbledore's curses and turned to regard the new arrival with undisguised contempt. He amplified his voice with a Sonorus charm, letting his words ring across the entire battlefield. "What use are you here, you worthless waste of space? Come to watch your betters work?"
The goat Patronus drove forward and reached him, and the dark energy swirling in its vicinity recoiled from its presence. The ground, which had been erupting with roiling black mist only moments before, grew still, and that momentary stillness allowed Dumbledore to reclaim the upper hand in the contest of wills between them.
Being called worthless was one thing. Actually being worthless was another. The very fact that Aberforth could insert himself into a duel at this level was proof enough of his power.
At least that much could be said of him. The four Heads of House, for instance, could make no such claim.
They had come hoping to help Dumbledore surround and capture Grindelwald, but they had stalled out near Tom's position, unable to push further. The residual magical energy left behind by the colliding spells had thickened the very air into something dense and suffocating, like wading through a bog. Every breath was a labour. Joining the actual fight was entirely out of the question.
The Patronus reached Grindelwald. He extended one hand and released a searing burst of white light, dissolving the glowing goat slowly into nothing. Dumbledore's curse lashed across the gap, and Grindelwald met it with a Shield Charm of iron hardness, but the moment the spell connected, a crack split visibly through the shield's surface.
The next second, Grindelwald vanished from where he stood.
"Watch yourself, Aberforth!"
Dumbledore vanished too. Both men reappeared simultaneously before Aberforth Dumbledore, their magical threads snapping taut between them like a tripwire. Aberforth fed his own power into the web, and for a suspended moment, the three of them stood locked in a triangle of balanced tension, none able to move without exposing themselves.
"Ha! Hahaha!" Despite being pushed back by the two brothers, Grindelwald laughed with the abandon of a man who had nothing to lose. "Albus! Aberforth! Does this feel familiar?! This is exactly how it was at Godric's Hollow all those years ago! The three of us, pulling against each other! And what came of it?!"
"You lost what mattered most to you! And today will end the same way!"
Neither of the Dumbledore brothers had expected Grindelwald to dare invoke that night. The memory rose unbidden, and it hit them both like a fist closing around their hearts, crushing without warning. Their faces betrayed them, pain bleeding through before they could stop it, and the steady stream of magical energy pouring through their wands faltered.
Grindelwald's eyes lit with cold, sharp focus. His wand snapped upward in a single decisive motion, and the deadlock shattered.
"Crucio!"
The scarlet curse struck Aberforth full in the chest. His scream tore through the battlefield, and the sound of it jolted Albus Dumbledore back into himself. He turned on Grindelwald with an expression caught between fury and horror. "Have you not a single shred of remorse?"
Grindelwald smiled, and it was a smile of pure, easy contempt.
Remorse? Not a trace. Perhaps once, long ago, there had been something. But Ariana was now summoned into the learning space, she had become Tom's student, and it would not be long before she was restored to life entirely. There was nothing left to feel guilty over, which was precisely why he could invoke her name so carelessly, using the memory like a blade to break the brothers' concentration.
And it was not only Grindelwald who was unmoved. Even Ariana herself, listening from within the learning space, had barely reacted to his words. Her death all those years ago had not been Grindelwald's fault alone. Both of her brothers had been in the thick of it, too consumed by their own fight to notice her. How could she hold an outsider to a standard she could not hold them to?
There was blame enough to share between all four of them. She had been wrong to wander into the middle of a duel. But her state of mind at the time, fractured as it was by the Obscurus within her, had been far beyond her control. The truth was that her death was too tangled, too complicated for simple blame. Every single one of the four people present that night carried a share of it.
"Come then, Dumbledore! Let it out! Use the wand's true power! I can feel how much you're holding back! Fill it with your rage and let it loose! Unless you'd rather watch me kill your brother right in front of you!"
Grindelwald had become something feverish, unhinged, hammering without pause against the most fragile place in Dumbledore's armour, the one wound that never fully closed: family. He drove his foot into the earth and the ground rippled like disturbed water, and Aberforth was launched high into the air and hurled away into the distance.
At the same time, Fawkes was still locked in combat with them. The three fierce fire-birds that had been steadily consumed and diminished suddenly merged back together, reconstituting themselves into pure, undiluted flame, and they rained down toward Hogwarts like a shower of falling stars.
Dumbledore moved to intercept the sudden shift in attack, but Grindelwald flung a silver chain that coiled and locked around him, pinning his hands long enough to deny him the reach he needed. Fawkes shrieked and shot forward at extraordinary speed, sweeping behind Aberforth and catching him before he could fall, but the fiery meteors streaking toward the castle were beyond the phoenix's reach.
Professor McGonagall, who had been in the middle of lecturing Tom about running out onto the battlefield without permission, snapped to full alert. "All of you, together! We have to stop those flames!"
The four Heads of House raised their wands in unison, the tips igniting with golden light. They reversed their grips, pooling their magic, attempting to cast Finite Incantatem in a combined effort.
"Professors, allow me. You can go back to deducting house points afterward."
Tom was already a step ahead of them. His wand rose in a clean, precise arc, his magic moving with the ease of thought. "Heaven and Earth, Reverse."
An invisible pulse expanded across the entire battlefield in an instant, and the world seemed to hold its breath for half a heartbeat. The fire meteors, which had been hurtling toward the castle at killing speed, stopped dead in midair, then turned, and drifted silently back up into the sky, where they hung motionless, suspended and harmless.
Every professor present stared.
The same fierce flames that even their combined casting of Finite Incantatem could not have stopped with any certainty had been frozen solid by a single quiet word from Tom.