The black flames writhed like living snakes, consuming the very air as the figure fully emerged from the dimensional rift. Marco felt the heat from his desk, a heat that didn't burn the skin but did burn the soul.
The sense of danger he had just purchased exploded in his mind like fireworks. The back of his neck wasn't just tingling; it was burning with warning.
[Customer identified. Updating information...]
The screen flickered frantically:
║ CLIENT ASSIGNED #002 ║
Name: Muzan Kibutsuji Universe of Origin: Kimetsu no Yaiba ( Demon Slayer) Danger Level: ⚠️⚠️⚠️⚠️⚠️⚠️ (CRITICAL) Power Level: Primordial Demon / Demon King Specialty: Biological Transformation, Absolute Regeneration, Demon Creation Reason for Visit: Search for solar immunity Available Resources: 3,800,000 MC
CRITICAL WARNING:
He has personally murdered over 100,000 humansCreator of the entire demon raceUnstable Psychology / God ComplexProbability of attempted manipulation: 98%DO NOT TRUST UNDER ANY CIRCUMSTANCES
Marco read the name and felt his blood run cold.
"No. No, no, no. TARS, tell me this is a joke."
[Unfortunately, no. And before you ask: no, you can't refuse. Rule number four.]
"He's a genocidal maniac! A literal monster who turns humans into flesh-eating demons!"
[Correct on all points. And yet , he's your client.]
The black flames finally dissipated, revealing the man—or creature—behind them.
Muzan Kibutsuji was... beautiful. Disturbingly beautiful.
Jet-black hair impeccably styled. Porcelain-pale skin. Crimson eyes with vertical pupils like a cat's. He wore a perfectly tailored, jet-black Western suit with an immaculate white shirt. He looked like a successful businessman, someone who could grace the cover of a business magazine.
Except for the eyes.
Those eyes held millennia of madness, power, and an insatiable thirst for perfection.
Muzan surveyed the shop with a mildly interested expression, like a collector appraising antiques. Then his eyes fell on Marco.
And Marco felt as if ice needles were being driven into every nerve.
Muzan 's voice was soft, polite, almost hypnotic. "A shop that exists outside of time and space. An entity that can even contact me." A smile appeared on his face, revealing perfectly white teeth. "And the owner is... a human."
It wasn't a question. It was an observation. An observation laden with barely contained contempt.
Marco swallowed, forcing his voice to remain steady. Years of dealing with difficult clients in the market had taught him a crucial lesson: never show fear, even when you're terrified.
"Welcome to The Multiversal Store ," Marco said, standing up. His newfound physical condition helped him maintain a straight, confident posture. "I'm Marco Antonio Durán, the owner. How can I help you today, sir...?"
" Kibutsuji ," Muzan finished , walking slowly toward the desk. Each step was measured, predatory . Kibutsuji . Though I have many names. Demon King. The Primordial Demon. The Catastrophe. The Chosen One." His eyes gleamed. "God."
"God," Marco repeated, maintaining his neutral tone. "Interesting title. I know several clients who also consider themselves gods."
Muzan 's eyes .
"Are you mocking me, human?"
[Marco, be careful. His temper is extremely volatile.]
"Not at all," Marco replied quickly. "I'm simply stating that this shop caters to all types of customers. Gods, demons, humans, and everything in between. Here, everyone is treated with the same professional respect."
Muzan reached the desk, placing his hands on the surface. Marco noticed that his nails were slightly pointed, sharp. Barely restrained claws.
"Professional respect," Muzan murmured . "What a... human concept." He leaned forward. "Tell me, Marco Antonio Durán, do you have any idea what I'm capable of?"
"Yeah."
The simple answer seemed to surprise Muzan .
"Yeah?"
"Yes. He's a demon with biological transformation capabilities. He can regenerate from almost any damage. He's existed for over a thousand years. He's created an entire race of demons under his control. And he's desperately searching for a cure for his only weakness: sunlight."
Muzan 's face darkened dangerously. The air in the tent grew heavier, almost suffocating.
"Watch your words, human. The word 'desperately' implies weakness."
"It involves motivation," Marco corrected, refusing to back down even as every instinct screamed at him to run. "And motivation is what brings customers to my shop. You're here because you want something. Something you haven't been able to obtain in your world despite all your power."
Silence.
Muzan stared at him with an intensity that would have made most people faint. Then, slowly, a smile appeared on his face.
"You're audacious. Stupidly audacious. But audacious." He straightened up. "Very well. Let's play your game, merchant. Yes, I seek immunity to the sun. I have sought it for a thousand years. I have experimented on thousands of humans. I have created hundreds of demons hoping that one will develop a resistance I can absorb."
"AND?"
"And none have succeeded. The curse that made me what I am is absolute. The sun is my only real weakness. And I will not tolerate weaknesses."
Marco nodded, activating the store interface.
"I understand. TARS displays options for the category IMMUNITIES - WEAKNESSES ELIMINATION."
[Charging...]
The screen behind Marco lit up with a new catalog:
║ ELIMINATION OF CRITICAL WEAKNESSES ║
CATEGORY: SOLAR IMMUNITY (Dark Beings)
OPTION 1: Daywalker Vampire Adaptation
Origin: Blade UniverseEffect: Complete solar immunity + maintains nighttime powersCost: 2,000,000 MCSide effects: None known
OPTION 2: Amaterasu 's Blessing
Origin: Japanese Mythology (Earth-777)Effect: Transformation into a being of dual light/darknessCost: 2,500,000 MCSide effects: Possible personality change towards benevolence
OPTION 3: Kryptonian Evolution Serum
Origin: DC Universe (Earth-52)Effect: Absorption of solar energy as a power sourceCost: 3,200,000 MCSide effects: Enhanced regeneration, exponentially increased strength under sunlight
OPTION 4: Blue Moon Ritual
Origin: The Originals (TVD Universe)Effect: Breaks solar curse permanentlyCost: 1,800,000 MCRequirement: Sacrifice of a doppelganger (can be provided)
OPTION 5: Solar Nanomachines
Origin: Metal Gear (Earth-919)Effect: Complete technological protection against solar radiationCost: 1,500,000 MCSide effects: Dependence on technological maintenance
Muzan read the list, his eyes moving rapidly. Marco could see his mind working, calculating, evaluating each option.
Kryptonian Serum ," he finally said. "It would make me more powerful under the sun."
"Correct."
"But it would also fundamentally change my biology."
"That's correct too. It wouldn't technically be a demon anymore. It would be something new. Something that has never existed in their universe."
Muzan drummed his fingers on the desk, considering.
"And the Daywalker Adaptation ?"
"It would retain its demonic nature intact, only eliminating the solar weakness. No fundamental changes to what it is."
"Disadvantages?"
Marco consulted mentally with TARS.
Daywalker Adaptation is purely defensive. It provides no additional benefits beyond eliminating the weakness. The Kryptonian Serum would turn the weakness into a strength.]
" Daywalker is purely defensive," Marco explained. "It eliminates the problem but adds nothing new. The Kryptonian Serum would turn their greatest weakness into their greatest strength."
Muzan smiled. A smile that didn't reach his eyes.
"And the price of that power is almost all of my resources."
"Three million two hundred thousand MC. You have three million eight hundred thousand available. You would have six hundred thousand left for other purchases if you wish."
"And you win...?"
"Fifty percent commission. One million six hundred thousand MC."
Muzan laughed. It wasn't a pleasant laugh. It was the sound of someone who finds humor in cruelty.
"You're honest about your greed. That's... refreshing. Most humans pretend to be altruistic while hiding their avarice."
"There's no reason to pretend," Marco said. "This is a business. You get what you want, I get paid. Simple."
"Simple," Muzan repeated . Then he straightened up completely, his expression turning cold. "Very well. I'll buy the Kryptonian Serum . But I have one additional condition."
Marco felt that tingling of danger intensify.
"What condition?"
"I want unlimited access to this store. I want to be able to return whenever I want. And I want..." her eyes gleamed with hunger, "...for you to sell me the method for creating more demons like me. Perfect demons. Immune to sunlight from the start."
[Marco, ALERT. This is extremely problematic.]
Marco's brain worked at full speed. His businessman's instincts were battling against his human morality.
Muzan solar immunity was already questionable. Muzan would use it to be more effective at hunting and killing humans.
But giving him the ability to create an army of demons immune to sunlight...
That would be genocide on a massive scale.
"Mr. Kibutsuji ," Marco said carefully, "I need to clarify something about this shop."
"Oh?"
"I can sell you power. I can sell you immunity. I can sell you almost anything. But there are limits."
Muzan 's eyes narrowed.
"Boundaries?"
"Moral boundaries that I set as the owner. And creating an army of demons immune to sunlight crosses that line."
The air in the store turned freezing. Literally. Marco could see his breath condensing.
"Do you dare deny me?"
"I'm not denying you service," Marco said, his voice steady even though his heart was pounding. "I'm denying THAT specific request. I can sell you your personal immunity. I can even give you future access to the store. But I'm not going to facilitate mass genocide."
[Marco, this is dangerous. Very dangerous. But... I respect your decision.]
Muzan stood motionless for a moment that seemed to last an eternity. Then he began pacing around the desk, circling Marco like a shark.
"I'm misunderstanding something," he said in a dangerously soft voice. "You're a merchant. Merchants sell. They don't judge."
"Good businessmen know when a deal is going to ruin their reputation," Marco replied. "If I sell you that ability and you create your army of demons, what do you think other customers will think? Customers who could be heroes? Demon hunters? Gods protecting humans?"
Marco turned to continue looking Muzan in the eyes.
"My shop is just getting started. My reputation is all I have. And I'm not going to tarnish it by being known as the merchant who facilitated the demonic apocalypse."
Muzan stopped. He stared at him. Then, to Marco's surprise, he smiled. A genuine smile.
"Clever. Very clever. It's not morality. It's business strategy."
"It's both," Marco admitted. "But if you need it to be purely business to accept it, then yes, it's strategy."
Muzan considered this, his fingers drumming in an irregular pattern.
"Okay. I accept your terms... with one modification."
"Which?"
Kryptonian Serum now. But in the future, if I find a way to create my army on my own without your direct help... you won't interfere."
Marco thought about this. Technically, if Muzan found his own solution, that wouldn't be Marco's responsibility.
"I'll try. But on my own terms."
"Bold. Speak."
"If you ever sell, trade, or give away anything you purchase from my store to others with the intent to cause mass harm, your access to the store will be permanently revoked."
Muzan frowned.
"That significantly limits what I can do with my purchases."
"You can use everything you buy however you like. But you can't turn my store into your personal arsenal to equip others. Deal?"
There was a long silence. Marco could feel the weight of the decision pressing down on both of them.
Finally, Muzan extended his hand.
"Deal."
Muzan 's hand was as cold as ice, and his fingers tightened enough to break normal human bones. Fortunately, Marco's athletic condition allowed him to withstand it without flinching.
[TRANSACTION CONFIRMED][Debit: 3,200,000 MC] [Credit: Kryptonian Evolution Serum + Future Access][Owner's Commission: 1,600,000 MC][SECOND SALE COMPLETED!][SPECIAL RESTRICTION ACTIVATED: Muzan Client] Kibutsuji - No transfer of purchased items]
A flask appeared floating between them. It was about the size of a fist, filled with a liquid that looked like liquid sunlight. It glowed with a warm, golden light that made Muzan instinctively back away.
"Concentrated light," Muzan murmured with a mixture of fascination and repulsion. "Ironic that my salvation comes in the form of my damnation."
"That's life," Marco said, carefully taking the bottle. "Solutions rarely come in convenient forms."
He handed the vial to Muzan , who took it with trembling hands. Marco had never seen the Demon King show anything resembling nervousness, but there he was.
"How is it administered?"
[Direct intravenous injection to the heart. The transformation process will take approximately 72 hours. It will be extremely painful. I recommend a safe and private location.]
Marco relayed the information.
Muzan nodded slowly, carefully placing the flask in his jacket.
"Seventy-two hours of vulnerability. Enough time for my enemies to find me if I'm not careful."
"Do you have a safe place?"
"Several. I have centuries of experience hiding." A crooked smile. "Although I won't need to hide much longer."
She turned to leave, but stopped in the doorway.
"Marco Antonio Durán."
"Yeah?"
"You're the first human in a thousand years to deny me something... and survive." He glanced over his shoulder. "I don't know if that makes you brave or stupid. But I respect it. When I return—and I WILL RETURN—I expect you to maintain that level of... integrity."
"I will do that."
"Good." Muzan began walking toward the reopening dimensional rift. "One last thing."
"Yeah?"
"In your shop, the rules protect you. Outside of it..." her eyes flashed crimson, "...other customers may not be as understanding as I am when you refuse them something. Be careful, merchant. The multiverse is full of beings who do not respect 'integrity'."
And with that, he disappeared in an explosion of black flames.
Marco stood there, staring at the empty space where Muzan had been. Then, slowly, very slowly, he slumped back into his chair.
His hands were trembling.
"TARS..."
[Yes, Marco ? ]
"I almost just caused the demonic apocalypse."
multiversal commerce .]
"Oh really?"
[Most multiversal traders would sell nuclear weapons to children if the price were right. You rejected millions of potential MCs on principle. That... is remarkable.]
Marco rubbed his face with his hands.
"It didn't feel remarkable. It felt terrifying."
[Because you were aware of the consequences. That makes you different. Dangerously different.]
"Dangerously?"
[Merchants with morals are unpredictable. Transactions based purely on greed are easy to calculate. But you…] TARS paused, "…you make decisions that sometimes go against your own best interest. That makes you harder to manipulate. And in the multiverse , that can be both a strength and a weakness.]
Marco checked his updated balance:
Multiversal Credits: 1,910,000 MC
Almost two million. In two sales.
And each one had left a mark on his soul.
Loki had given a precious memory of his mother.
Muzan ... Muzan had been a test of how much Marco was willing to sacrifice for money.
"Are all customers going to be like this?" Marco asked. "Moral tests disguised as transactions?"
[Not everyone. Some will just want to buy a cool sword . Some will want food from their home world. But the important clients, the ones who change destinies... yes. Those will always be tests.]
A notification appeared on the screen:
[Client Loki ] Laufeyson has completed 150 hours of study. Time remaining: 50 hours. Requests brief hearing with owner.
Does Loki want to talk?
Muzan 's presence . The gods are sensitive to that kind of evil power.]
"Let him in."
The study door opened. Loki came out, and Marco barely recognized him.
He had spent 150 hours—more than six days—studying the Grimoire. His hair was disheveled. There were dark circles under his eyes. But those same eyes shone with a power Marco had never seen before. Runes covered his arms, visible even through his armor. The air around him bent and rippled as if reality itself was having trouble containing him.
"Marco," his voice resonated with powerful harmonies, "what the hell did you just let into your store?"
"The Demon King from another universe."
"And did you sell it to him?"
"I sold him solar immunity."
Loki stared at him. Then he began to laugh. A long, almost hysterical laugh.
"You're crazy. Completely crazy. Do you have any idea what a demon immune to sunlight can do?"
"Yes. That's why I denied the second part of his request."
"Was there a second part?"
Marco told him about the demon army. Loki stopped laughing.
"You told him no."
"I told him no."
"You said no to a being that could kill you with a thought."
"The store rules protect me in here."
"And outside?"
Marco shrugged, trying to appear more confident than he felt.
"I'll have to be very careful about when and where I leave the store."
Loki watched him for a long moment. Then he approached the desk and placed his hand on Marco's shoulder. The gesture was surprisingly gentle coming from the God of Lies.
"Marco Antonio Durán, I don't know if you're the bravest human I've ever met or the most stupid. But for what it's worth..." his eyes shone with sincerity, "...if that demon or any other client tries to hurt you outside these walls, just say my name. I swear by Asgard I'll come."
Marco felt a lump in his throat.
"Why? You barely know me."
"Because you treated me like a person, not a god or a monster. Because you were honest even when it would have been easier to lie. And because..." Loki smiled sadly, "...because someone who refuses to sell genocide even when it would benefit them financially is someone worth protecting. There are very few of you in the multiverse ."
"Thank you, Loki ."
"Don't thank me yet. I have fifty more hours of study. When I'm done, I'll be dangerous. Maybe as dangerous as your demon client." His eyes flashed with determination. "And then, when I face Thanos , I'll have the tools to win. Or at least to make him pay dearly for every blow."
"You're going to win."
"Your faith is... comforting. Even if it is naive." Loki headed back to the study. "Rest, merchant. You look like someone who just aged ten years in an hour."
And he disappeared behind the door.
Marco leaned back in his chair, mentally and emotionally exhausted.
[Marco, I suggest you rest. You have a room available from the owner. Comfortable bed, full bathroom, even a small kitchen with food from your world.]
"I'm hungry?"
[You haven't eaten in six hours of store time. Your improved body requires more calories. Yes, you're hungry.]
As if TARS's words were a signal, Marco's stomach growled.
"Okay, okay. Where is that room?"
A door materialized in the wall, labeled simply: OWNER
Marco approached and opened it. On the other side was a surprisingly cozy room. It wasn't huge or ostentatious. It was... homey. There was a queen -size bed with sheets that looked like clouds. A small desk with a laptop (why would he need a laptop in a multiversal store ?). A bathroom visible through another door. And a small kitchen with a stove, refrigerator, and...
"Is that a coffee maker?"
[From your favorite Mexican coffee brand. Café de Olla. We also have ingredients to make tacos, if you want something family-friendly.]
Marco felt tears sting his eyes. It was a small detail, insignificant in the grand scheme of things. But at that moment, after negotiating with a god and a demon, after almost facilitating a genocide, after everything...
Seeing that coffee pot with coffee from his homeland felt like a hug from his mother.
"Thank you, TARS."
[You're welcome. Now eat, sleep, and process what you learned today. Because tomorrow...]
"What about tomorrow?"
[Tomorrow you begin your real training. You have money. You have basic skills. But if you're going to survive in Middle-earth, if you're going to handle more clients like Muzan , you need to be more than just a merchant.]
"What do I need to be?"
[Dangerous. You need to become dangerous enough that customers think twice before crossing paths with you. Not just here, where the rules protect you. Outside. In the real world.]
Marco nodded slowly, entering his room.
"Then tomorrow I become dangerous."
[Exactly. But tonight, just be Marco. Eat tacos. Drink coffee. Remember who you were before all this. Because that person, that taco vendor crying over Cruz Azul, is the core of who you need to keep being.]
"What if I lose it? What if all this power changes me?"
[Then I will have failed as your assistant. My job isn't just to help you succeed, Marco. It's to make sure that when you succeed, you're still you.]
Marco closed his bedroom door, went to the kitchen, and started making tacos al pastor for the first time since his death.
As the meat cooked, as the familiar aroma filled the air, as his hands followed movements he had made thousands of times...
Marco Antonio Durán cried.
She wept for her family, whom she would never see again. She wept for Loki and the memory he sacrificed. She wept for the impossible choices she would have to make. She wept because in one day she had earned almost two million multiversal credits ...
And he felt poorer than ever.
But when she finished crying, when she wiped away her tears and served herself her perfectly made tacos...
She smiled.
Because I could still make tacos. I could still cry. I could still feel.
He was still human.
And as long as he was human, there was hope.
[END OF CHAPTER 5]