The monitors floated in a loose arc before the throne, each one a pane of pale light, each one showing a different corner of the Great Tomb of Nazarick.
Ainz sat with his elbow on the arm of the throne and his chin resting on his bony fist, and watched the first floor of his home go quiet.
It was a graveyard. It had always been a graveyard. Rows of weathered headstones stretched away under a perpetual starlit sky, with low mist curling around their bases and the occasional gleam of a skeletal hand poking out of the earth. Somewhere in the dark a zombie shuffled in a slow circle. A skeleton warrior leaned against a crypt, motionless, waiting.
It was extremely atmospheric, and it was extremely cheap.
"The outer layers are running exactly as designed, Lord Ainz," Albedo said. She stood a precise step behind and to the left of the throne, her white gown pooling around her feet, her golden eyes moving over the screens with the calm attention of a general reading a map. "The first three floors are maintained by Shalltear's undead and the POP spawns. The cost to Nazarick is nothing but the mana already in the system."
"Nothing," Ainz echoed.
"Nothing beyond what was already allocated by the Supreme Beings."
"Good."
"The Fifth and Sixth Floors are, as you know, more expensive." She did not need to say why. They had been widened, at enormous cost, years ago, so that the system would accept the tomb as a valid dungeon. Ainz still remembered what the gold had looked like leaving the treasury. "The Seventh Floor is Demiurge's. The Eighth is... reserved. The Ninth is the residential level. The Tenth is where we are now."
"I remember the layout, Albedo."
"Of course, Lord Ainz." She bowed, very slightly. "I only wished to be thorough."
Ainz let out a breath he did not need. He had spent the last three days in this room, going over the defense system floor by floor, and every time he looked at it, the same uncomfortable thought crept back.
The last time invaders walked the halls of Nazarick, they had been workers from the Empire.
They had come in through the front gate, and they had died. Not all of them at once, and not in any very interesting way, but they had died in the graveyard and in the crypts and in the traps that Albedo had laid out for them, and when they were dead, they had stayed dead. That was the point. That was the whole premise on which the Great Tomb was built. An intruder who walked in stayed in. An intruder who died did not come back.
It was a sound principle. It had kept Nazarick safe for years.
And three days ago, in a town called Wegmark, Ainz had watched a girl in a mage's robe get clubbed by an ogre, flash into a column of white light, and vanish.
She had come back an hour later with a bruise on her pride and nothing else.
"Albedo," he said.
"Yes, Lord Ainz?"
"Suppose that an invader walks into the first floor. Suppose that he is a very capable, very determined invader. Suppose that Shalltear's undead kill him."
"He would be killed, Lord Ainz."
"And suppose that an hour later he walks back through the front gate, entirely unharmed."
For the first time in the conversation, Albedo did not answer at once.
"I beg your pardon?"
"He returns," Ainz said. "Every time. An hour after he dies. With no injury and no penalty. And with everything he learned in the last attempt."
The line of Albedo's mouth tightened, very slightly.
"That would be a considerable problem," she said slowly.
"Yes."
"The traps would be of limited use. An intruder who survives long enough to study them would eventually overcome them."
"Yes."
"And any trap with a cost, poison gas, floods, summoned hordes, would drain the treasury faster than we could replenish it." Her golden eyes were very sharp now. She had stopped looking at the monitors and was looking at Ainz. "Lord Ainz, is this a hypothetical?"
"It is a... situation I have encountered," Ainz said carefully.
"In the other world."
"In the other world."
"I see," Albedo said. She folded her hands in front of her. "I shall prepare a full analysis."
"Thank you."
"I will have it by morning."
"There is no need to hurry."
"Lord Ainz," said Albedo, with a faint, tender smile, "you have not slept in three days."
"I am a skeleton."
"You have not rested in three days," Albedo corrected. "And you are staring at the same monitor you have been staring at for the past four hours."
Ainz looked at the screen. It was still the first floor, still the graveyard, still the same bored skeleton warrior leaning against the same crypt.
"I find it very calming," he said, a little defensively.
"Of course, Lord Ainz."
"It is very well designed."
"It is," Albedo agreed. "By the Supreme Beings."
They both looked at it in silence for a while.
"It was never built," Ainz said at last, quietly, "for people who come back."
***
Thursday came, as Thursdays did.
At sundown, a small purple gateway flickered open in the Great Hall, and Leah and her party stepped through with baskets. Lyla carried a stack of ledgers and a faintly guilty expression, which Ainz had learned meant she had been working on the way over. Blanc carried a tin of cookies and a very small wooden doll, which she held in one hand like a talisman. Leah carried the tea.
"Satoru!" Leah said, brightly. "You look terrible."
"I appreciate your honesty."
"I mean you look like someone who's been awake for three days."
"I have been reviewing a document."
"Have you slept?"
"I am a skeleton."
"That's not what I asked," Leah said, but she was grinning, and she took the seat at his right hand without waiting to be invited. "Okay, so what's up? You've got the look."
"What look?"
"The one you get right before you ask me something that sounds casual and isn't."
Ainz considered denying it. Then he considered how thoroughly Leah had learned to read him, and chose to take another route.
"I have been thinking about Wegmark," he said.
"Okay."
"About the girl in the forest who died."
"Oh," said Leah. "Yeah. Respawns are weird the first time you see them."
"I find them... fascinating."
"Really?"
"I find them," Ainz said, with the rigid calm of a man trying to ask a question without sounding as though he cared, "extremely instructive."
Lyla, who had been arranging her ledgers on the table, stopped.
"Ah," she said. "That's what this is."
"What is what?"
"You're doing math."
"I am not doing mathematics."
"You've got the face of someone who's doing mathematics," said Lyla.
Ainz did not have a face. He had a skull. But there was, apparently, some quality in the angle of it that Lyla had learned to read, and he found it a little unnerving.
"Fine," he said. "I wish to understand how it works."
"How what works?"
"The respawn," Ainz said. "In its entirety. What happens when a person dies, what they lose, what they keep, and how they return. And also..." He hesitated. "How it works for you."
"For me?"
"For your army."
Leah's smile faltered for a moment.
"My army," she said.
"The ants. The undead. The mountain cats. The knights in the adamantite armor." Ainz folded his hands. "You have a very large number of subordinates, Leah, and I have never once seen you worry about losing them."
"I do worry," Leah said.
"I have never seen you worry about the cost."
Leah looked at him for a long moment. Then she looked at Lyla, who raised one eyebrow, and at Blanc, who was too busy trying to feed a cookie to a doll to pay attention.
"Okay," she said at last, slowly. "I can explain it. But you're not going to like the answer."
"Why not?"
"Because it's going to make you very, very jealous."
***
"It's called the Retainer system," Leah said.
She had taken a napkin from the table and was drawing on it with a sharpened stick of charcoal she had produced from somewhere. It was a very bad drawing. It involved a large circle labeled LEAH and a number of smaller circles connected to it by lines.
"I'm the liege lord," she said. "The big circle. Everything else is a retainer. The ants, Sieg's undead, the cats, the knights, all of it. They're not monsters in the normal sense. They're characters bound to me by the skill."
"Bound."
"As in, they follow my orders, and the system treats them as part of my retinue."
"Go on."
"Here's the important part." She tapped the napkin. "When a retainer dies, they respawn after a timer. An hour, for the ones I've tested. They come back where they died, or somewhere nearby, with all their stats. And there's no penalty."
"No penalty," Ainz said.
"None. When a player dies, they lose ten percent of their EXP. It's brutal. Retainers don't. They just come back."
"And the cost?"
"What cost?"
"The cost of bringing them back," Ainz said, very carefully.
"There isn't one."
He sat quite still.
"I beg your pardon?"
"There's no cost," Leah said. "I don't pay anything. No gold, no crystals, no items. I don't have to cast a spell. They just come back when the timer runs out."
"Every time."
"Every time."
"Indefinitely."
"As long as I'm alive," Leah said.
Ainz did not move. Somewhere in the Great Hall, Sebas set down a teapot with exquisite care, as though the sound of it hitting the saucer might shatter the silence.
"And their experience?" Ainz asked.
"That's the clever bit." Leah's voice had gone a little softer, almost shy, as though she were describing a favorite hobby. "Retainers can't earn EXP on their own. Everything they kill, everything they do, the EXP goes straight to me. So the more they fight, the stronger I get, and nobody loses anything on the way."
"They die," Ainz said slowly, "and they return, at no cost, and they bring you experience every time."
"Yes."
"And you may send them out as many times as you wish."
"As often as I want."
"For as long as there is something to fight."
"Right," said Leah.
"Leah," Ainz said, in a very small voice. "That is not a trick. That is... that is an economy."
"I told you you'd be jealous."
"I am not jealous."
"You're gripping the table."
Ainz looked down. His gauntlets were wrapped around the edge of the table, and the wood beneath them had begun, very faintly, to creak.
"I am simply... reflecting," he said, and released it.
"On what?"
"Every NPC in Nazarick is irreplaceable," Ainz said. "Every one of them was made by a Supreme Being and cannot be remade. If one of them dies, they are gone. There is no timer. There is no return." He paused. "I have spent my entire time in this world trying to avoid losing a single one of them. And you are telling me that you do this with your entire army every day."
"It's not exactly every day," Leah said.
"How often?"
"Pretty close," Leah admitted.
"And there is no cost."
"There's a cost," said Leah.
"What is it?"
"I'll tell you," Leah said, "but not yet. It's a long story, and honestly I'd rather show you."
Ainz stared at her.
"Show me," he repeated.
"I want to take you to the dungeon. The one under the World Tree, I mean. You should see it in action." She smiled. "It's the easiest way to explain it."
"There is a dungeon?"
"Sure. It's the main thing we do. Humans keep coming."
"Humans," said Ainz.
"Vault Holders, mostly. Loads of them. Different parties every day, different guilds, new faces every week. They hear that the Harbinger's lair is full of loot and good EXP, and they show up. They fight. They die. They respawn. Then they come back for more, or somebody else shows up and does it for them. It never ends."
"They are never the same people."
"Almost never," Leah said. "I've had the same guild three times in six months, but mostly it's fresh blood."
"And they do not know."
"Know what?"
"That you are a player," Ainz said. "That the Harbinger of Destruction is a person behind a screen."
Leah's face went very still.
"No," she said quietly. "They don't. That's the one thing that absolutely can't get out."
"I understand."
"If the Vault Holders figure out there's a player on the monster side, they'll stop treating the dungeon like a dungeon. They'll start treating me like a target."
"Yes."
"And the rest of my people... Lyla, Blanc... everyone's tied into this. If it breaks, it all breaks."
"I will not speak of it," Ainz said.
"I know you won't." Leah smiled, a little crookedly. "That's why I'm showing you."
Lyla, who had said nothing during this exchange, was looking at Ainz with an expression he could not read.
"You should be careful," she said, at last. "I know what you're thinking."
"What am I thinking?"
"You're thinking about how to use it."
"I am thinking," said Ainz, "about how to protect it."
"That's the same thing, with you."
"It is not," said Ainz, and then, because he was a man who tried to be honest, "...it is occasionally the same thing."
"That's what I thought."
"Lyla," said Leah.
"I'm only saying."
"We're friends."
"I know," Lyla said. She looked at Ainz for another moment, and then, unexpectedly, she smiled. "I'm only saying that he has a very good head for logistics. And it's going to be very difficult to keep it out of this."
"I would consider that a compliment," Ainz said.
"It was meant as a warning."
"I know," said Ainz. "I am taking it as both."
***
The tea ended late.
Blanc had fallen asleep with her head on the table and the little wooden doll tucked under her chin, snoring faintly. Aura and Mare had carried her out, one on either side, with Mare holding the doll very carefully. Demiurge and Lyla had stayed behind long enough to exchange two notebooks and a very long, silent look.
Ainz stood alone in the middle of the Great Hall with his hands folded behind his back, watching the last of the candles gutter.
"Lord Ainz."
Albedo had come up quietly. She stood at his shoulder, her white gown trailing, a thick sheaf of papers in her arms.
"I thought you were preparing an analysis."
"I have prepared the first draft." She held out the papers. "I wished to give it to you before you retired. Though I understand that you will not."
"I am a skeleton."
"Yes, Lord Ainz." She smiled. "I know."
He took the papers. They were covered in her small, neat handwriting. A series of diagrams. A table of estimated costs. A list of assumptions, numbered one to forty-three, the first of which read: Invaders may return.
"This is very thorough," he said.
"I am eager to improve our defenses."
"You have been awake for three days as well."
"I am a succubus."
"That is not the same thing as sleeping."
"It is a little the same thing," said Albedo, with great dignity.
Ainz looked down at the pages. He turned one over, and then another. At the bottom of the fifth page, in a small, tidy box, she had written a question.
What is the cost of a defense that does not end?
"Albedo," he said.
"Yes?"
"I believe I have been asking the wrong question."
"Which question, Lord Ainz?"
"I have been asking how to stop invaders who return," Ainz said, slowly. "But I do not think that is the point. I think... I think that the people who return are not the problem. I think it is the fact that I have never once considered what it would mean to have a defense that never runs out."
Albedo said nothing. She waited, in the way she had learned to wait for him, with her head slightly bowed and her hands folded in front of her.
"Leah's army costs her nothing," Ainz said. "Nothing. And mine costs me everything."
"Lord Ainz..."
"I am not saying that mine is worse. I am only saying that they are... different. And I wish to know why." He looked up, at the tall dark windows of the hall, at the stars beyond them. "She has agreed to show me. Tomorrow, or the day after. I do not know. But I wish for you to come."
Albedo's eyes widened.
"To the other world?"
"To the dungeon. Under the World Tree." He paused. "As my consultant. If you are willing."
For a moment, Albedo did not speak at all. Then she bowed, very deeply, her black hair falling forward across her shoulders.
"It would be," she said, in a voice that was not quite steady, "the greatest honor of my life."
"It is only an inspection."
"It would still be the greatest honor of my life."
"Albedo."
"Yes, Lord Ainz?"
"Please try not to burn anything down."
"I will do my very best," Albedo said gravely.
Ainz looked at her, at the neat sheaf of papers in his gauntlets, at the empty hall around them with its flickering candles and its sleeping banners. He thought of an ogre, and a girl who vanished, and an army that came back.
Somewhere deep in the tomb, a skeleton warrior leaned against a crypt, waiting for invaders who would never return.
For the first time in a very long time, Ainz found himself hoping that someday they might.