Dumbledore
You must kill me. I ask this one great favor of you, Severus, because death is coming for me as surely as the Chudley Cannons will finish bottom of this year's league.
"Murderer!"
Severus turned from Bill Weasley's unconscious form and saw Seamus Finnigan, bruised and puffy, hurtling toward him. The boy's wand was half-raised, but with a wordless flick of his wrist Severus sent him flying headfirst into the nearest wall.
Impulse control had always been Finnigan's problem, he thought in some isolated corner of his mind, watching the boy crumple in a pathetic heap on the floor. With half a brain and a smidgen of self-control, the fool could have avoided most of the bruises that currently distorted his face. Snape had given him openings all year, fleeting chances to back down or at least to take the thinking man's option of sabotage rather than public defiance. But the idiot was incapable of shutting his mouth, and he'd kept crossing the only lines Snape had been able to draw, throwing himself to the wolves that waited beyond them.
They were all the same, these Gryffindors, always shouting out their rage instead of planning their attacks, and managing to bleed all over him in the process. Snape raised his wand over the unconscious child, anger and disgust twisting his face. No one who ran at an enemy shouting 'murderer' rather than 'stupefy' had any business being in combat, and Snape was about to ensure that Finnigan wouldn't wake up for a very long time.
Snape nearly joined the boy in a much longer sleep as a jet of red light brushed against his skin, scorching his cheek. He whirled around, automatically pushing a shield charm out in all directions, and it shuddered under the impact of twin 'reducto' curses. Snape sighted along their line of fire, his eyes trailing up the great staircase, and his throat clenched in a painful spasm as he met horribly familiar blue eyes. There was no time for anything else.
The corridor and stairwell lit up like a fireworks explosion, the air between them so thick with spell and counter-spell that it seemed a wall of light. The duelists were both moving, Aberforth plowing down the stairs like a force of nature and Snape gravitating to the nearest open doorway, angling himself to take advantage of its meager shelter. They had no words for each other, save for an inarticulate yell that seemed to be pouring out of Aberforth without his knowledge. They needed no incantations. Aberforth did not share his brother's brilliance, but he was ancient and powerful. And he did not waste his rage in bitter words, but let its power fuel his curses, which tore apart Snape's doorway with disturbingly little difficulty.
Forced into the open, Snape stepped forward as Aberforth rounded the base of the staircase. Snape blocked three hexes in quick succession – for all his skill, Aberforth was no Occlumens – and slashed his wand upwards. Aberforth's wand flew out of his hand.
The old man stared at him in shock. It had happened too fast. For a moment he looked as if his anger would carry him forward, even weaponless, but there was too much ground between them – Snape could cut him down long before he got close. Dumbledore let out a long breath, followed by a low and bitter laugh. "The both of us, then," he said, and waited.
Snape pointed his wand at Aberforth's chest and stared at him unblinkingly for several long seconds, murmuring under his breath. Aberforth frowned, feeling no spell. Then, unbidden, his most recent memory of Harry Potter, standing with his mates outside the Room of Requirement, floated to the top of his mind.
Confusion shaded Aberforth's eyes, and then a new rage flared as he clamped them shut, raising his hand to cover them like a child playing hide-and-seek. But the damage was done, and he knew it. Cursing, he dropped his hand. "I should have known, you and your bloody mind games! That's your only trick card, isn't it? And it's won you every round." He shook his head, the torches shining white in his grimy spectacles. "He should have thrown you in Azkaban that night I caught you sneaking about," Aberforth whispered.
Snape said nothing, but thought: Yes. He should have.
"I wish I'd thrown you headfirst down those stairs," Aberforth said. "I wish I'd snapped your worthless neck all those years ago."
Yes, Snape thought, I wish you had.
"If wishes were horses," he answered aloud, and his voice was cold and smooth.
I'd take any death before that night. Snape began to move. I'd take it from the werewolf, I'd take it from my father, I'd take it from you in your dingy stairwell – and she'd be breathing now.
Snape swung his wand forward violently, and a burst of light sped toward Aberforth.
But your brother wouldn't be. No death of mine could save him.
The spell threw Aberforth backwards like a rag-doll, so familiar. But he did not have far to fall. He landed on the flagstone floor, and Snape's boot shoved him disdainfully into the shadows under the stairwell where no one would notice the gentle rise and fall of his chest. He'd be out for a few hours at most, hopefully time enough for Snape to find Potter.
Snape heard a scream from somewhere above him, some idiot Gryffindor, no doubt, without the sense to keep her mind on her own problems. He glanced up, but saw no immediate threat. His robes snapping behind him, he set off for the seventh floor corridor.
He was halfway there when Lucius caught up with him, and told him his presence was required elsewhere.