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Detecting the acrid stench permeating the air, Erwin grimaced and sprinted toward the bathroom.
Within moments, he reached the entrance to the girls' bathroom and heard thunderous footsteps echoing from within.
Without hesitation, Erwin charged through the doorway.
The creature that greeted him was nightmarish.
Twelve feet tall, with gray, dull skin stretched over a grotesque frame.
A disproportionately small head sat atop a massive, lumpy body. Tree-trunk legs supported its hulking mass, ending in bare feet covered with thick calluses and grime.
A young witch had been backed into the corner, so paralyzed with terror that she couldn't even scream.
It was Hermione.
Watching the troll advance toward Hermione with lumbering steps, Erwin raised his wand without hesitation.
"[Oppugno]!"
Loose stones and debris from the floor rose into the air, organizing themselves into a swarm before pelting the troll's skull.
Erwin deliberately moderated his magical output; he didn't dare use too much force for fear of sending the troll flying directly into Hermione.
Just enough intensity to capture the creature's attention.
The troll felt the assault from behind and turned around with awkward, jerky movements.
Its primitive brain struggled to process what had happened.
After several confused moments, it began stomping toward Erwin with earth-shaking steps.
When the troll had nearly reached him, Erwin cast another spell.
"[Petrificus Totalus]!"
The Full Body-Bind Curse took hold, freezing the troll in place.
At the same time, Erwin quickly circled around the immobilized creature and reached Hermione's side.
Seeing Erwin's arrival, Hermione finally released the breath she'd been holding, and quiet sobs escaped her throat.
But Erwin had no time to comfort the frightened girl.
The troll's naturally high magic resistance meant the petrification wouldn't last long; the creature would break free within moments.
Sure enough, just as Erwin positioned himself in front of Hermione, shielding her with his body, the troll's massive frame began to tremble.
It was about to break through the spell's constraints.
Now that Hermione was safely behind him, Erwin could fight without restraint.
He leveled his wand at the struggling troll.
"[Confringo]!"
Erwin showed no mercy. A high-powered Blasting Curse shot from his wand tip.
Pure magical effects inflicted minimal damage on trolls, and Dark Magic would be inappropriate to use here.
The only way to harm the creature was through the physical force generated by explosive spells.
The troll took the full impact of the Blasting Curse.
A massive shockwave sent the creature hurtling through the air, smashing clean through the bathroom wall and flying into the corridor beyond.
The crude wooden club it had been carrying flew from its grip, spinning end over end through the air.
Seeing the airborne club, inspiration struck.
Erwin pointed his wand at the tumbling weapon.
The wooden club began transforming mid-flight, reshaping itself into a gleaming silver sword with a wickedly sharp edge.
"[Depulso]!"
The advanced Banishing Charm made objects shoot toward targets at tremendous velocity.
The transfigured sword flew like a legendary weapon blessed by the gods themselves, streaking toward the troll.
Everything happened within two seconds.
Before the troll could land, the blade struck it squarely in the throat, then pinned the creature to the corridor wall.
****
"Merlin's beard!"
An exclamation rang out from beyond the bathroom.
The voices sounded like Professor McGonagall and Professor Flitwick.
Seeing the troll secured against the wall and knowing the professors had arrived, Erwin finally allowed himself to relax.
Looking at Hermione, who was still sobbing quietly, Erwin gently wrapped an arm around her shoulders and guided her out of the destroyed bathroom.
Sure enough, Professor McGonagall, Professor Flitwick, and Professor Snape stood just outside.
They'd been about to rush in when Erwin emerged with Hermione.
Then Professor Quirrell appeared as well.
He took one glance at the impaled troll before crouching on the ground and whimpering pathetically.
Snape's eyes flicked from Erwin to the troll pinned to the wall, his expression unreadable.
Professor McGonagall had gone deathly pale.
"What on earth were you thinking?"
"Mr. Gaunt, and Miss Granger, I require an explanation immediately!"
Professor McGonagall's voice trembled with equal parts fear and anger.
Two first-year students had engaged a fully-grown mountain troll in combat.
Everyone knew that while trolls weren't particularly intelligent, their naturally high magic resistance made them notoriously difficult opponents even for adult wizards.
Professor Flitwick had been equally worried at first, but seeing both students unharmed brought visible relief.
He walked over to examine how they'd managed to kill the troll.
"I apologize, Professor. We were... spending time together. We didn't know a troll had entered the castle. I had no choice but to fight it."
"Spending time together? In the girls' bathroom?!"
Professor McGonagall's voice rose three full octaves.
She couldn't believe what she was hearing. 'Are young students really this bold nowadays?'
"Yes, Professor. It's a quiet location with few visitors," Erwin replied without the slightest trace of embarrassment.
Snape gave Erwin a look that was equal parts mockery and grudging respect.
Professor Flitwick regarded Erwin with a stern expression.
He knew how Erwin and Cho were close, of course.
Hermione, still held in Erwin's protective embrace, flushed a bit.
She understood perfectly well that Erwin had invented this excuse to shield them both from Professor McGonagall's punishment.
It was still embarrassing, though.