They found their footing together faster than Kevin expected.
Harry was not Kevin. He didn't have Kevin's peculiar arsenal, his five years of compounded impossibilities. What Harry had was something different — an absolute directness of purpose, the quality of someone who has decided they don't have anything left to lose and has found that terrifying fact oddly liberating.
Kevin threw a fireball volley at Voldemort. Harry, reading it, drove a smoke screen into the aftermath before Voldemort could regain his sightlines. Voldemort cleared the smoke with a wind-burst and found two dozen fireballs hanging around him in a ring.
They went off simultaneously.
"Shadowless Blade!"
Harry's invisible cutting hex tore through the firestorm toward the smoke. It connected.
"Chain Lightning!" Kevin waved his hand. Fire spears shot through the arcs of Harry's lightning, riding the current as guidance, and hit Voldemort in a cluster.
The look on Voldemort's face — that precise moment of processing how rapidly the dynamic had shifted — was one Kevin privately catalogued for later.
They drove him back. Harry's water shields became platforms as much as defences; Kevin bounced off them, cut in from the flank, bounced away before Voldemort's retaliation could track him. Voldemort couldn't focus on both of them simultaneously, and each time he redirected, the other one was already moving.
The Avada Kedavra on the sword tore at him every time it connected. His spells were losing cohesion. The soul that had been pieced together from so many fragments was coming apart at its seams.
And then Voldemort made the calculation that Kevin had been half-expecting.
He went for Harry.
It was the logical move — the weaker target, the one whose loss would break Kevin's composure. Voldemort streaked across the valley floor, wand levelled, covering the distance in a second.
Kevin was already moving.
He hit Voldemort from behind with the full weight of the crowbar and the full charge of the Avada Kedavra enchantment in a single combined strike. The impact launched Voldemort forward. He crashed into the rock face near Harry, half-embedded in the stone, head down.
Harry's eyes lit up. He raised the Gryffindor sword.
"Harry — wait —"
Harry lunged.
The blade went through.
Voldemort's chest. Clean through. The sword of Gryffindor, plunged into the Dark Lord's heart.
Harry's grin lasted exactly as long as it took for Voldemort's eyes to open.
The smirk on that pale, ruined face was the worst thing Kevin had ever seen.
"Avada Kedavra."
The wand was jammed against Harry's chest. Green light, point-blank range.
Kevin threw himself forward.
His hand closed on empty air.
The curse fired.
Harry flew back.
Kevin stood in the echo of it with his hand still reaching, and the valley was suddenly very quiet.