The Fiendfyre Curse.
Among wizards, it was also known as the Devil's Flame.
It had earned that name mainly because it was widely recognized in the magical world as an evil flame.
What made Fiendfyre so terrifying was that it could take the form of monsters and relentlessly hunt down anything that could burn, regardless of friend or foe.
At the same time, it was an extremely easy spell to lose control of.
Of course, if that were all, it would not have earned such a fearsome reputation.
The main reason was that the Fiendfyre Curse had once left behind a spectacular and unforgettable achievement in wizarding history.
Or rather, the wizard who had used it had a rather special identity.
That piece of history was this.
The Fiendfyre summoned by the previous Dark Lord, the dark wizard Grindelwald, had very nearly burned the entire city of Paris to the ground.
That was an important magical capital, not some small village.
The horrifying sight of the whole sky seemingly set ablaze, together with the raging fire that spread across the entire city, had taught every wizard a harsh lesson.
So the Fiendfyre Curse was truly that dangerous.
It was after that incident that the Fiendfyre Curse became a spell forbidden from unauthorized use, especially in cities.
But Draco had not expected that he would actually have the chance to see Fiendfyre inside Hogwarts Castle.
And the Fiendfyre before his eyes was completely different from the Fiendfyre Curse he had used during the Triwizard Tournament.
Because the Fiendfyre he had used had not gone out of control.
"But... who cast that Fiendfyre Curse?"
...
Raging flames were devouring everything in sight.
Wherever the tongues of fire reached, everything turned to ash.
Almost nothing could withstand such flames.
And Harry Potter was struggling desperately under the assault of the Fiendfyre Curse.
"Do you like fire, Harry Potter?"
"Ahahahahaha!"
Such terrifying flames could not help but remind people of the Fiendfyre Draco had used during the Triwizard Tournament.
Of course, Harry Potter, who had been transported away halfway through the tournament, had not personally witnessed that great feat or the wondrous sight. He had only heard about it from others and imagined the scene from their descriptions.
But this time, he was personally experiencing what it felt like to be chased by fire.
Naturally, Harry Potter had not failed to think of fighting back.
Facing the Fiendfyre behind him, Harry Potter turned around with a fierce expression and drew his wand. "Clear Spring Water Charm!"
Harry Potter's shout certainly sounded impressive.
But the result was far from satisfying. The jet of water that shot from the tip of his wand evaporated the instant it touched the air, vanishing under the intense heat.
Because of that brief pause, more than half of Harry Potter's robes were burned away.
If he had not reacted quickly and torn the robes from his body at once, Harry Potter might already have been swallowed by the flames.
Seeing this, Harry Potter realized that this was no ordinary fire.
Watching Harry Potter's foolish attempt, Amycus Carrow let out a shrill laugh. "So this is the Chosen One everyone talks about? How disappointing."
"Stop running. If you obediently come back with me to see the Great Master, I'll spare your pathetic little life!"
Although he said that, Amycus Carrow showed no sign of easing up. Surging magic continued pouring into the wand in his hand.
The flames began to change shape, turning into a great swarm of beasts made of fire, fire snakes, and fire Dragons.
They rose, fell, and rose again.
Centuries' worth of accumulated junk was thrown into the air, dropped into their fanged mouths, or fell beneath their clawed feet, only to be swallowed by the hellish blaze.
This Amycus Carrow seemed to have forgotten that his Master wanted Harry Potter alive, not a lump of charcoal made from Harry Potter himself.
Fortunately, this room appeared far larger on the inside than it did from the outside, with plenty of corners and open spaces for Harry Potter to dodge the fire monsters chasing him.
The piles of clutter scattered around also served as useful cover, helping Harry Potter evade the Fiendfyre's attacks.
That was what allowed Harry Potter to continue clinging to life under such an assault.
"How? Where did it go wrong?!"
While enduring the agony in his lightning-shaped scar, Harry Potter looked at Amycus Carrow's appearance with suspicion.
This room was the Room of Requirement. How had the other man found his way here?
Had Aberforth lied to him?
"But... does this count as a lucky accident?"
He did not know whether it was his imagination, but from the burning pile of debris, there seemed to come a shrill scream and a strange wisp of black mist.
It was this abnormality that made Amycus Carrow, who had been cackling only a moment before, freeze.
For some reason, he had the feeling that he had caused serious trouble.
Harry Potter seized that chance. While the other man was distracted, he rushed toward the room's only exit.
But even Harry Potter himself did not notice that when he looked toward the debris, a strange meaning flashed through his eyes.
It looked like relief, and also like regret.
The thick smoke and heat were suffocating.
The moment Harry Potter opened the door, he saw several familiar figures appear before him.
Once he recognized them, he let out a great sigh of relief.
"Professor Lupin!"
"Harry!"
"Come with me."
There was no time for catching up. Professor Lupin, who had only just arrived, immediately grabbed Harry Potter by the arm and led him running back the way he had come.
It was not only because this was no time to talk, but also because the Fiendfyre surging toward them forced Lupin to give up on asking anything.
Fiendfyre that had reached this scale was no longer something that could simply be extinguished.
And so, the uncontrolled flames, after devouring generations of contraband hidden by students, swallowing the sinful results of countless forbidden experiments, and consuming the countless secrets people had hidden inside this room, spread directly into the corridor.
This was the scene Draco and the others saw.
Before the flickering flames could reach them, the thick smoke swept in first, like a black dragon.
In that instant, before anyone could react, their vision was completely taken away.
Chaos.
Inside those flames that could devour everything, Draco could hear the screams of wizards one after another.
Under normal circumstances, there might indeed have been a chance to stop it.
But while both sides were locked in battle and holding each other back, stopping Fiendfyre like this was nothing more than wishful thinking.
Draco covered his mouth and nose with his robes and watched the rolling smoke and the fire monsters rampaging about. His brows drew tightly together. "We have to stop this... otherwise, before that person even attacks, Hogwarts will be gone first."
He understood the situation.
But the problem was that these frenzied Death Eaters had to be dealt with first.
"Damn it, break through!"
"No! These Death Eaters have no intention of letting us get out alive!"
"Think of something, Alastor. Our magic is almost spent!"
"What about breaking through the wall?"
"This is the eighth floor, and once we're in the air, we'll just be targets for them!"
It could be seen that the Death Eaters, who clearly had no intention of letting this opportunity pass, had instead intensified their assault. They showed no sign of stopping because of the great fire before them.
Even Alastor Moody had not anticipated such a sudden turn in the situation.
And at that moment, Draco saw a certain figure appear among the members of the Order of the Phoenix.
"Is that... Potter?"
From Harry Potter's battered and weakened appearance, Draco immediately understood that someone seemed to have used the Fiendfyre Curse on him.
The next second, Amycus Carrow appeared as well, his body also covered in several burns. Accompanied by his hoarse, shrill laughter, he launched another suicidal attack.
"Fiendfyre!"
"Damn it, is that madman trying to drag us all down with him?!"
"Stop him!"
Fiendfyre was definitely not a gentle Charm.
Nor was it a Charm just anyone could control.
More often than not, it ended with both the target and the caster being harmed.
Just as Draco decided to remove the Disillusionment Charm and try to interfere with the battle before him, Snape, who had likewise gone unnoticed, slowly drew his wand. From his lips came the one sentence that made Draco freeze.
"Don't act. I imagine you have something more important to do."
"..."
"Do not forget, I am now the Headmaster of Hogwarts, Severus Snape!"
"Godfather?!"
Before Draco could figure out when he had been exposed, Snape slowly took a step forward.
Draco, who had been about to ask something, closed his mouth.
As the fierce wind blew in through the window, Snape's black robes snapped like a cloak.
His arms rose with force, opening slightly to either side as if he were about to summon something.
At that moment, Snape gave off an inexplicable, strangely sacred feeling.
Then Draco heard Snape's hoarse shout.
"Awaken, Hogwarts!"
"Piertotum Locomotor!"
The moment this spell, which had never been recorded in any magical text, came to an end, Draco felt the entire castle beneath his feet begin to tremble faintly, as though it had come alive.
The repeated rumbling sounds were like heavy objects striking the ground.
"What are those?!"
It was not until the orderly sound of marching footsteps came that Draco understood where the noise was coming from.
Because he was standing at the outermost edge of the corridor, Draco was the first to see what had happened.
"This is the highest level of Transfiguration Spell!"
What appeared before Draco's eyes were stone soldier statues, one after another.
They were marching toward this place in perfect order.
One step.
Then another.
Dozens, hundreds, thousands... From the scale of the commotion, Draco could roughly judge how many of these stone soldiers there were.
These stone soldiers, holding all kinds of weapons and shields, seemed to descend from above as if answering a summons.
Was this Hogwarts' trump card?
I command you all to advance, my loyal... warriors!