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What did Master mean when she said that I had given her the answer to the “Last Door”?
As if to answer my confusion, Master removed her hat and spoke.

“Remember, when you were still a child, how Marlene once dropped my teacup?”

Did that really happen?
I think it did.
Or maybe it didn’t…

“At that time, I wondered: Marlene hadn’t used any magic or strength at all, yet the cup shattered to pieces. Where did such destructive power come from?”

Now that she mentioned it, I vaguely recalled a conversation like that.

“You said then, ‘Things that are high up already hold great power.’”

Yeah, I don’t remember it.

I was probably talking about potential energy, the kind of thing you learn in middle school science.
A teacup sitting on a shelf has potential energy.
Drop it, and that potential energy is converted into kinetic energy, shattering the cup.
That’s all it was.

But from my fragmented explanation, Master had somehow grasped the whole concept.
Energy isn’t born from nothing—it’s there from the start, unseen.
It took her less than half a day to reason out the existence of thermal energy and chemical energy on her own.
She wasn’t called the Great Sage for nothing.
Come to think of it, that was right around when Master started studying destructive and teleportation magic—spells outside her specialty.
Back then, we disciples all thought she was just eccentric, but apparently it was for the sake of studying physics.

“At that moment, I thought: perhaps mana too is one such form of energy. Perhaps life itself as well.”
“Life too?”
“Indeed. From the moment it is born, life begins to fall. Its momentum increases until, on the final day, it strikes the ground and shatters.”

I see—she was comparing the flow from life to death to the conversion of potential energy into kinetic energy.

“A shattered life is indeed no longer life. But that force of life has not disappeared. It simply changes form, still existing somewhere else. If so, what is there to fear in death?”

With those words, Master set down her staff and opened a door.

Inside was a small chamber. Pale blue light flickered faintly, illuminating the room. It was quiet, yet I felt an ominous current of mana in the air.
The floor bore a magic circle. It was an old design, marked with outdated and inefficient sigils.
The entire circle was glowing faintly blue. The glow seemed to come from the circle itself.

Master stepped into the center.

“This is the magic circle I use to supply myself with mana for life support. From here, I will shut it down and open the ‘Last Door.’ You will enter as well.”
“Me too?”
“Yes. For ‘safety.’”

Was it really safer inside the magic circle?
I stepped cautiously into the circle as told. The density of mana inside was so high that casting carelessly could trigger a runaway.

“Now then. Whatever happens, do not leave this circle. Understood?”
“Y-yes.”

Once I nodded, Master began chanting an incantation I had never heard before.
The circle grew brighter and brighter.

“Ugh… gh…”

Master grimaced and clutched her throat.
At the same time, the mana in the room began to move.
A massive whirl of energy formed around us.

Bracing her small feet, Master declared in a firm voice:

“Death is not the end. It is but one current in the cycle of power. Death, bow before me.”

The whirling mana began to shine, unstable energy bursting into light.

“Master!”

I shouted as the entire chamber was engulfed in a flood of radiance.
A dangerous sign.

“Fear not… I…”

Though she was right beside me, her voice sounded far away.
Should I stop the ritual? It shouldn’t be too late.
But I held my ground, trusting her.

Eventually, the torrent of light subsided, leaving only the circle itself glowing.
Thanks to my werewolf eyes, the darkness only made the glow more blinding. I still couldn’t make out Master’s state.
But I noticed the room had grown cold.
My breath turned white. Frost clung to the walls and floor.

Then the light died completely.
Within the faintly glowing circle, Master still stood. She looked unchanged—perhaps only a little paler.
But the instant I saw her I knew: Master had completely transformed.

She raised her hand, and the temperature plummeted. Glittering specks danced in the air—diamond dust, formed as the moisture in the air froze.
She was probably absorbing the heat in the air.

“So… it has come to this.”

She murmured, then looked at me.

“I have come to understand life as simply one of many forces. Life is power, and power is life. Thus, by drawing in other forms of power, life may be spun anew.”

Lowering her hand, the drop in temperature ceased.

“No longer shall I trouble others with mana exhaustion. And few, if any, could hope to defeat me now. This is the ‘Last Door’ I have passed through.”

In short, Master had become a “vortex” that absorbed… not just mana, but all forms of energy—vitality, magical, even physical strength—drawing them in and consuming them.
She had transcended both life and death.
For at the center of a vortex, nothing exists.

I squeezed my words,

“M-Master… you’ve become something outrageous…”
“You understand, then.”

She smiled.

“To me now, the lives of others are but masses of power. You know what that means?”
“I do.”

To her, every life, every ounce of heat, was food.

Not only that—
From flame, she could take heat. From arrows, kinetic energy.
She could neutralize enemy attacks, absorb their energy, and turn it for her own benefit.
It was absurdly overpowered.
Master had always been able to drain mana—she’d even drained the false heroes’ weapons. But to think it would go this far…

“Uh, Master…”
“What is it?”
“Does this mean… even a Hero couldn’t defeat you anymore?”

I asked nervously. She gave a bitter smile and shook her head.

“This Vortex is not so grand. Its purpose is recovery, nothing more. If I try to draw in something too great, I myself cannot withstand it. A Hero’s power could still destroy me.”

So there were limits to what she could absorb.

“The greater danger is to my own mind. Human and demon lives alike are now nourishment to me. That could well erode my very self.”
“Please don’t! I’d hate that.”

A crazed Demon Lord? Unthinkable.
But Master laughed.

“As long as bonds remain with those around me, I shall not indiscriminately consume lives. Marlene is a vampire, yet she does no such thing, does she?”
“Well, I guess so.”

She cleared his throat, glancing at me from the corner of her eye.

“So… you understand, don’t you?”
“Understand what?”
“You thickheaded boy. You must all pamper me and fuss over me, so I don’t go astray.”
“Like how we always do?”
“Y…yes. Exactly.”

She looked a little disappointed, but went on.

“Of course, I’ve prepared a safeguard.”
“What kind of safeguard?”

“When you stood with me inside the circle, the vortex came to recognize you as part of itself. Therefore, it cannot draw power from you.”
“Wait—does that mean…?”

Master beamed a smile.

“Precisely. No matter how strong the blow, only your attacks can harm me. A single bite of your fangs could end me.”

Why would she deliberately create such a weakness?
Ah. I understood.

“If ever I drown in power, or crumble under the weight of it—”
“Master, no.”
“—I would have you end me with your strength.”

I knew it came down to this.

“Fret not. Even if I and the vortex were to vanish together, you will remain untouched. It only recognizes you as a part, not truly so.”
“That’s not what I’m worried about.”
“If I must perish, I’d rather it be by the hand of my beloved disciple.”

How could I refuse it if you said it like that?

But was it really all right for her to entrust something so grave to someone like me?

“What if I lost myself to ambition and tried to strike you down for power’s sake?”

At which, Master sighed in exasperation.

“What a foolish question. You would never do such a thing.”

No, that blind trust only made me more uneasy, you know?

“If you, who are without greed, ever raise your hand against me, then there must be a just cause. In that case, I’ll submit and vanish into the void.”

No, no, no.
Don’t make it sound that easy.

“Mm. A fine idea, if I say so myself. The comfort of knowing someone trustworthy will stop me if I falter… for a king, what greater reassurance could there be?”

For me, it was nothing but anxiety.

“It is a fitting duty for the Demon Lord’s Vice-Command, don’t you think?”
“W-well, yes…”

Just like that, I’d been saddled with a responsibility far heavier than I ever wanted.