"NOOOOO!"
A woman's shrill scream filled the air, heavy with anguish, but this voice did not belong to Oleandra, nor to Hermione, nor to any of the female students or teachers. Rather, it belonged to someone on Voldemort's side… Bellatrix.
Voldemort stared at an unharmed Harry with hatred mouldering in scarlet eyes, even as his body crumbled to ashes. His serpentlike eyes remained fixated on him as what little remained of his blackened soul squirmed free from his crumbling mortal shell, and the pillar of brimstone that made up his weakened form shot into the air, streaking deeper into Hogwarts.
"Harry!"
Harry's friends rushed to his side as he stood there, looking rather lost as he stared into empty space. The Death Eaters were running away now, while the Heliopaths simply remained where they stood, looking every bit as confused as Harry now did… but not all of the Death Eaters were fleeing.
Spotting the golden badge that forced the Heliopaths to obey its holder's command in a pile of Voldemort's ashes, Oleandra reflexively shoved her hand into her pocket, a Summoning Charm already forming on her lips, but her wand remained cool to the touch as her fingers closed around it, rather than buzzing with its familiar warmth.
"Accio Serving Seal!"
The golden badge flew into Rookwood's waiting hand…
"Expelliarmus!"
…only to fly from his grip as Harry struck him with a scarlet beam of magic.
"Crucio!" Bellatrix bellowed, taking aim at Oleandra as she dived to catch the badge.
Oleandra braced herself as crimson lightning arced along her sword and licked across her body, yet, oddly enough, it brought only a faint, tickling sensation. With a roar, she tore free of the red sparks and cleaved through Bellatrix's neck, severing her head from her shoulders in a single, decisive stroke. Bellatrix's eyes were filled with shock, sorrow, and fury even as her head flew in a wide arc above the battlefield, before striking the ground with a dull crack and rolling to Nott's and Rookwood's feet.
By now, the fleeing defenders had noticed that the battle had somehow taken a turn for the better, and they turned on their heels and swarmed back across the Entrance Hall, firing potshots at any Death Eaters they could see.
"I have the Serving Seal!" Oleandra proclaimed, raising the golden badge high above her head. "Heliopaths, hear and obey! Capture the Death Eaters!"
The Death Eaters stood no chance as their former allies turned on them at once, obeying the orders of the Serving Seal's new owner without hesitation. Within minutes, not a single one of the black-robed, silver-masked Wizards and Witches remained conscious, so thoroughly were they outnumbered by Oleandra's thralls and the brave defenders of Hogwarts.
With the Heliopaths now at her beck and call, now Oleandra had the opportunity to do something rather amusing, such as declaring herself the new ruler of the British Wizarding World and siccing them on anyone who dared resist, but after a brief moment's consideration, she tossed the Serving Seal to Kingsley Shacklebolt, who looked very relieved.
"We won," Ron said numbly. "We actually won."
Oleandra barely had the time to sheathe Excalibur before Fred and George lifted her and Harry onto their shoulders, shouting, "Three cheers for our heroes! Hip, hip, hurrah!"
A great cheer erupted from the defenders.
"HIP, HIP, HURRAH!"
"Wait, it's not over yet!" Harry shouted over the cheers, tapping Fred's shoulder. "We haven't won yet!"
"How did you even live through a second Killing Curse?" Oleandra asked dizzily. "I saw you get hit by the light…"
"It's because he took your blood!" Harry exclaimed.
The first of Voldemort's many mistakes was rebuilding his corporeal form using Harry's blood, further binding their fates together.
Initially, Voldemort viewed his prophesied enemy as his greatest foe, and thus the ritual using Harry's blood had brought him back at maximum power. Through the shared blood running through their veins, they had become something akin to family, sharing Lily Potter's sacrificial charm between themselves. This allowed Voldemort to touch Harry without turning to ashes… but it also strengthened the protective magic shielding Harry; Voldemort unwittingly kept Lily's sacrifice alive with his every heartbeat.
However, something that not even Dumbledore could have possibly predicted ended up happening… a Christmas miracle. Oleandra awoke from her coma just as Voldemort triumphed over Harry and his friends, having lured them to St Mungo's with a fake Ron. But just as he was about to win, Oleandra took him by surprise, and she destroyed his mortal form, thus ruining Dumbledore's carefully laid plans.
At this point, Oleandra had beaten Voldemort twice.
In his arrogance, Voldemort decided that poor, powerless Harry was not actually his greatest foe; rather, it was Oleandra, who had defeated him in a manner he could actually accept and understand: through her own magical prowess, rather than the saccharine self-sacrifice of others or mere luck.
Until the very end, he never even considered love a valid form of magic.
The second time his body was destroyed, his followers knew for a fact that he was immortal, so they did not desert him or go on self-destructing crusades that got themselves pointlessly arrested. They held a second ritual to revive him, but instead of using Harry's blood, they used Oleandra's… thus tying his fate to hers.
That was Voldemort's second and greatest mistake.
Accustomed to being the centre of attention, Voldemort never even considered the possibility that Oleandra might not regard him as her greatest enemy, yet she was powerful in magic and openly hostile to him, and so using her blood allowed him to regain most of his magical strength.
… that is, until Oleandra lost all her powers.
When she sacrificed her runes, every last drop of magic in her veins abandoned her, and as she and Voldemort were ritually bound through blood, so did most of his magical potency desert him, twice over; for how could the dark ritual or Voldemort himself possibly consider a powerless Muggle girl his greatest enemy?
When Voldemort used the Killing Curse on Harry, Lily's sacrificial charm once again activated to protect her son. No magic lasts forever; after sixteen long years, one might have expected its potency to dwindle away to nothingness, but thanks to Voldemort carrying Harry's blood for three years, its life expectancy had been somewhat extended… enough to completely rebound the weakened Killing Curse onto its caster.
Even though Voldemort was protected against his own magic by Viviane's incomplete sacrificial charm, it was a charm powered by the soul rather than blood, and so his fractured soul was too weak to ward off the rebounding Killing Curse, and his physical form was once again destroyed.