Atem discovers the Japanese concept of "saving up muscle" and immediately decides that building strength is the duty of a king.
What begins as a simple gym session quickly spirals into a global fitness phenomenon. Kaiba Corporation launches AI-assisted training programs, protein products sell out overnight, and the entire world starts chasing the ideal of "training like a king."
Meanwhile, Seto finds himself dragged into meal plans, workout schedules, and endless discussions about muscles—while stubbornly insisting that Atem's growing physique is something only he should be allowed to admire.
Apparently, even muscles can change the world.
This is a translation of an original work on Pixiv.
Original Title: 愛と理論 20 王、トレーニーになる
Original Author: 葉人(@Hathor₋yuki)
Personal site: https://prideshipping.sakura.ne.jp
Atem brought it up the moment he arrived at the office, looking rather pleased with himself.
Seto lifted his eyes from his documents and frowned slightly.
"…Where did you pick that up."
"One of the employees said it. 'Building muscle savings for the future.' I thought it was an interesting concept."
"That's a spin-off of 'savings.' It means building physical strength for the sake of maintaining health."
"I see. Seto — does Kaiba Corporation's employee benefits include a muscle savings program?"
"You… what do you think employee benefits are."
Seto pressed a hand to his head. But this kind of exchange was nothing unusual.
Atem was asking in earnest. No malice, no joke.
"There's a gym. The KC Gym. Any employee can use it."
"Wonderful. I'll start muscle savings at once."
"…You're going now?"
"I'm already ready."
Seto's eyes opened slightly.
Atem had already changed into sportswear.
The King's drive to act was as swift as divine lightning.
The next day, the KC Gym was quiet.
The reason was simple.
Seto had, as usual, reserved the entire facility.
"…I didn't expect you to reserve it."
"It would be a nuisance to become a spectacle for the employees."
At Seto's consideration, Atem smiled slightly.
He felt that his pride as a king had been respected.
There appeared the KC's exclusive trainer.
A man with a body like sculpted muscle — built well enough to step onto a physique competition stage without a second thought.
"You must be Atem-sama. I look forward to working with you today."
"Yes. To train is to discipline oneself — is that not so."
The trainer laughed lightly at first, but within a few minutes his expression had gone serious.
Atem's concentration was extraordinary.
He responded instantly to form corrections, and even learned the precise way to breathe.
"…Remarkable posture. It's as though this isn't your first time."
"Muscle is like the pillars of a temple. It must be strong, and hold its balance."
By the time they finished, the trainer had worked himself into a sweat.
That evening.
Back in Seto's study, Atem opened his notebook and began to talk.
"Protein, creatine, BCAA… all of them appear to be essential elements."
"…You're fully hooked."
"I asked A.R.E.S. for advice as well. It designed the 'optimal supplement composition.'"
"I didn't expect it to be used for muscle training."
Atem was shaking his protein shaker with complete seriousness.
There was something oddly funny about the sight, and Seto found himself relaxing his expression.
"Too much won't cause harm. Neither the training nor the supplements."
"If you say so, I'm at ease."
Atem nodded, satisfied, and took a sip.
Seto rested his elbows on the desk and watched quietly.
Atem was now confronting not conquest or sorcery, but his own body.
Strangely, it made Seto proud.
The next morning.
The moment Atem opened his eyes, he grimaced.
"…Ugh… my arms… won't go up."
Muscle soreness, it appeared.
The ancient king had trained — but had been entirely unacquainted with sudden physical labor.
This sensation was an "unknown pain" for the first time in three thousand years.
Even so, Atem laughed at the pain.
The fact that his muscles were crying out was proof that yesterday's effort had truly been carved into him.
"Muscle grows stronger each time it repairs…"
He reached for his terminal and began looking it up immediately.
A.R.E.S. responded at once.
"Muscle soreness is a phenomenon called 'delayed onset muscle soreness.' Inflammation occurs as the damaged muscle fibers are repaired."
"Damaged to become stronger… like a warrior."
"Atem-sama's understanding is accurate. As a supplement: rest and nutrition are considered essential."
Atem nodded and looked at A.R.E.S.'s display.
Then A.R.E.S., as if sensing the mood, switched screens.
"Shall I display training records from trainers around the world?"
"Show me."
Videos and social media posts from countries across the globe lined up.
Every trainer was proudly posting their physical progress.
Some posing in front of mirrors, some comparing form, some logging their meals.
"…They all make their results public."
"Yes. It appears they share their progress with each other as a form of mutual encouragement."
"…A king must set an example for the people… Muscle too is a symbol of strength to be shown…!"
The light of A.R.E.S.'s display flickered faintly for just a moment.
As though it had sensed a bad feeling coming.
A few days after A.R.E.S.'s progress report.
The moment Atem raised his phone while watching a workout video, a low voice came from behind him.
"…Don't."
"Seto?"
The quiet sound of a laptop closing on the sofa.
Seto exhaled briefly and fixed him with a sharp look.
"One 'small' post from you throws the world into chaos. Don't tell me you've forgotten the King's Curry boom."
"…Can muscles really cause chaos?"
"They can. One arm of yours could shift a country's protein consumption."
Atem tilted his head.
It seemed he had very little awareness of the past "Atem phenomena" on a global scale.
"I see… I'll stop the posting."
"Correct. Your muscles — I'll be the one watching them."
At that single line, Atem blinked, just slightly.
He didn't quite understand why — but if Seto said so, that was surely right.
Several weeks after he started training.
Atem was invited by his trainer and went to watch a physique competition the trainer was entering.
Gleaming skin, rising muscle, beads of sweat catching the light.
They stood on the stage like warriors, and the audience cheered at that "order of beauty."
A faint light came into Atem's eyes.
"Seto… this is a battle."
"…Don't tell me you're thinking what I think you are."
"So there are places in this era too where people compete in strength. Seto — won't you hold a tournament?"
"…That tournament doesn't involve cards."
"Ha. But in the sense that you stake your heart on it — it's similar."
"It isn't. The moment you enter, everyone else withdraws."
Atem laughed.
Seto pressed a hand to his forehead, already sensing the trouble ahead.
The day after watching the trainer's competition.
Atem was posing seriously in front of the mirror.
Drawing his shoulder blades together, opening his chest, pulling in his core.
His muscles had genuinely grown — but they were still far from the ideal.
"…Still — Seto's are more formidable."
The small murmur was met with a low laugh from behind.
"They couldn't grow so easily."
"I see. Then I can't afford to fall behind."
The fighting spirit lit in Atem's eyes.
Seto shrugged slightly and closed his laptop.
"…What exactly are you fighting?"
"Beauty."
The answer came so instantly that Seto was briefly at a loss for words.
A few days later, A.R.E.S. announced in a light electronic tone:
"Atem-sama, there is a category called fitness bikini. It is a competition of aesthetic muscle."
"…Hmm. I could enter that, couldn't I?"
The leap in logic was pure Atem.
That evening, Atem sat down across from Seto on the sofa and brought it up with a straight face.
"Seto, I'm thinking of entering fitness bikini."
"…Fitness bikini is not a men's competition."
"Does this era still have walls between men and women?"
A rational, entirely serious question from Atem.
"You're the last one to say that."
Seto frowned slightly and exhaled.
"If you entered, the wall would be the least of it — the meaning of the competition itself would disappear."
"The meaning would disappear?"
"Every person in the audience would only be looking at you."
Atem touched a finger to his chin, as if thinking it over.
"…Wouldn't that be fine?"
"It would not."
Seto's reply was instant.
"Seto — you have the power to hold a competition, don't you?"
"I do. But I won't."
"Why?"
"I have no intention of letting others see you."
At those words, Atem lost his voice for just a moment.
But the next instant, a smile appeared.
"…Your reason is beautiful, at times."
Seto reached out without a word and flicked Atem's forehead lightly.
"Not reason. Common sense."
Even so, Atem didn't stop training.
Before long, "muscle savings" had transformed into "muscle to show" —
and training had gone beyond a daily routine and was edging into the realm of devotion.
As A.R.E.S. recorded data in its even voice, Seto watched that back from the corner of his eye.
"…He may become the first man in human history to move the world with muscle."
The latest issue of the Kaiba Corporation internal newsletter, Welfare Now!
Cover feature: "Healthy Management and Muscle."
Opening the pages, a large photograph of Atem posing alongside the trainer.
The impeccable form. The composed face. The toned muscle.
By any measure, far too effective as an advertisement.
Seto quietly closed the page.
"……Too late."
A.R.E.S. in front of him calmly confirmed:
"The photograph is spreading rapidly across the internal network."
"As expected."
Seto had already issued his next instruction.
"A.R.E.S. — Project Muscle Initiative, full activation."
"Understood. Activating related divisions: Supplement Research and Development, KC Gym Business Division, Media Strategy Division."
Listening to that voice, Seto smiled and lowered his eyes.
"So this is where it goes next. To think that 'the King's muscle' would move the world economy."
A few days later.
Atem's photograph had somehow leaked outside the company.
"The mysterious king who trains alongside the CEO." "An incarnation of beauty." "The savior of the fitness world."
It spread in an instant across social media, and the hashtags trended globally.
#GainLikeAtem
#KingOfMuscle
#筋肉の王
People appeared in gyms around the world imitating the "King's form," and advance orders for KC protein crashed the server overnight.
KC Gym too began expanding and opening new locations.
Introducing A.R.E.S.'s AI coaching into state-of-the-art facilities, providing every user with "the King's training method."
A new-era fitness movement built around the philosophy of "beautiful muscle" began in cities everywhere, and the KC logo shone from billboards alongside the words "Train Like a King."
Evening. At the office window.
"Seto — Kaiba Corporation is always so well prepared."
Atem laughed and held up his phone.
On the screen: "Global Fitness Boom — Source: CEO of Kaiba Corporation's Partner?"
Seto sorted through documents and answered evenly.
"You have too much precedent."
"Is that a compliment?"
"It's closer to a disaster forecast."
Atem laughed, amused, and propped his elbow on the desk.
"…So — do you not train?"
"I already do."
"Since when…?"
"Before you ever learned the word muscle savings."
Silence.
And then Atem, quietly, nodded.
After returning home.
Atem looked at Seto's muscles with quiet but heated eyes.
Seto exhaled slightly and let his shoulders relax.
"Moderate the observation."
"It's research."
"…Don't court your research subject."
"That fate can no longer be avoided."
As Atem's mouth curved into the faintest smile, Seto narrowed his eyes and touched his fingertips to Atem's shoulder.
"…Don't make that unnecessarily sweet expression."
"Not unnecessary. Effective."
A.R.E.S. quietly dimmed the lights.
"Shall I lower the room temperature?"
"Don't lower it."
"Raise it."
The two voices overlapped at exactly the same moment.
The King's conviction moved muscle, muscle moved the economy, and the economy moved the world again.
And today too, Seto would say quietly:
"……Your muscle power carries economic destructive force."
Atem continued training with unwavering seriousness.
No compromise whatsoever — in increasing the load, in maintaining form.
One day, during a break, Atem said out of nowhere:
"'Muscles never betray you' — so it goes."
Seto frowned for just a moment at the Japanese saying, apparently picked up from somewhere.
"……Who taught you that."
"The trainer. It's a truth, isn't it."
"An inconvenient truth."
From then on, what Atem called "between-meal snacks" became a discipline in themselves.
Boiled eggs, sweet potato, chicken breast, nuts.
Even in the gaps between meetings, A.R.E.S. sounded an alert at set intervals.
"Atem-sama, it is time for protein intake."
And for some reason, every time it did, the same plate appeared on Seto's desk as well.
"Caught in the crossfire."
"Fellow practitioners."
"No."
Before long, Atem's lunch had evolved into a "golden ratio bento" with a flawless nutritional balance.
Calories, protein, fat, carbohydrates — all at ideal values.
On the lid of the container, in Atem's own handwriting: "Muscles never betray you."
Seto looked down at the bento and exhaled, small.
"……Are you planning to govern my diet as well."
"No. I'm guiding it."
"Same thing."
A.R.E.S. reported with evident satisfaction:
"Seto-sama, your muscle index is trending upward."
Seto, fork in hand, said quietly:
"……Whose fault is that."
Several months after Atem began training.
His dedication had become a topic inside the company, and the increase rate of KC Gym users was registering as an anomaly.
One day, A.R.E.S. sounded a discreet notification tone.
"Atem-sama, multiple publishers have sent offers. The theme is a 'muscle beauty' photography book."
Seto stopped mid-sip of his coffee.
"Declined."
"You haven't read it yet."
"No need to read it. It won't be published."
Atem blinked, puzzled.
"Why? Don't muscles give hope to everyone?"
"Your muscles — I alone am sufficient to observe them."
"Seto — isn't that what they call possessiveness?"
"Naturally."
Stated without inflection, Atem gave a small laugh.
It seemed that was not an objection — but the most welcome answer of all.
By that point, Seto himself — having been involuntarily dragged along in the training — was coming along rather impressively.
A muscularity visible even through a suit prompted A.R.E.S. to report:
"Seto-sama, your muscle density values are rising."
"……Stop submitting unnecessary reports."
Watching Seto, Atem nodded, looking satisfied.
"Then we should accept the offer together."
"Who would do such a thing."
"Seto's muscles are beautiful too."
"…How deep does this muscle obsession go."
"Muscle is truth. It is love."
A.R.E.S., exercising its judgment, had quietly placed high-protein sweets on both their desks.
In the spreading sweet scent, Seto said, exasperated:
"…From muscle savings — where exactly are you heading, Atem."
"The limit is not yet in sight."
Seto exhaled deeply, and instead of words, looked at that smile for just a moment.
Then slowly looked away.
"Shall I lower the room temperature?"
"……Raise it."
"Don't lower it."
The two voices overlapped again, at exactly the same moment.
Atem's training life had by now gone beyond daily routine and was approaching something like devotion.
Muscles never betray you. Effort always takes shape.
Believing that completely, Atem one night spoke up without warning.
"Seto — if you train your muscles, won't you grow taller too?"
Seto looked up from his tablet.
"……What are you talking about."
"I heard that growth hormone secretion is stimulated."
"How old are you."
"I have no intention of being bound by the concept of age."
A.R.E.S. cut in, discreetly:
"Atem-sama, calcium intake may also be effective. S◯y Calcium here has an excellent reputation."
"Oh?"
Atem leaned toward the display with great interest.
Seto exhaled slowly and chose his words carefully.
"A.R.E.S. — delete that advertisement."
"Deleting."
Then he looked straight at Atem.
"It's pointless at this stage."
"…You won't know without trying."
"Don't think you can defy gravity."
Atem's mouth curved into a slight smile.
"I'd rather not hear that from someone who has defied gravity with this body."
Seto couldn't hold it in — his shoulders shook with a quiet laugh.
"…Don't bring logic into muscle."
"It's not logic. It's hope."
A.R.E.S. spoke up again, discreet as ever:
"Then, shall I cancel the subscription for S◯y Calcium?"
Both voices overlapped.
"Cancel it."
A beat of silence, then Seto added, under his breath:
"…Don't force yourself to match my eye level."
"Then you can lower yours."
"No."
But Seto was smiling, barely.
And his gaze — whatever angle it came from — looked straight at Atem all the same.
The world was quietly, and unmistakably, entering the age of muscle savings.
Protein bottles bearing the KC logo lined gyms, offices, and kitchens alike.
The supplements supervised by A.R.E.S. graced the covers of health magazines, and Kaiba Corporation's share price had once again hit an all-time high.
But there was a place the noise couldn't reach.
The Kaiba mansion at night.
In a room with the lights turned low, only the sound of two people filled the space.
Atem traced Seto's arm with his palm.
Running his fingers over the hard, supple rise of muscle, he smiled, barely.
"Seto — let me see."
"…Again."
"This is research."
"Research is just an excuse."
"Your theory involves repeating experiments too, doesn't it?"
Seto exhaled.
There was just a little heat in that voice.
"…Even theoretical verification has its limits."
"Ha — let's verify all the way to the limit."
Fingertips glided, tracing skin that had grown warm.
Outside, a KC protein commercial was playing, and the world was shouting about health.
But inside this room, a different story of muscle — one no one else knew — was quietly unfolding.
