Atem discovers the concept of "relationship stagnation" through a wedding magazine and immediately decides it requires thorough research.
If long-term couples can lose their spark, then surely he and Seto must prepare in advance.
There is only one problem.
Neither of them has the slightest idea what "being bored with each other" actually feels like.
While editors become increasingly fascinated by their "Quantum Marriage," A.R.E.S. quietly records every failed attempt to recreate monotony, and Seto reaches only one conclusion:
Some relationships simply refuse to become ordinary.
This is a translation of an original work on Pixiv.
Original Title: 愛と理論 21 王、マンネリに備える
Original Author: 葉人(@Hathor₋yuki)
Personal site: https://prideshipping.sakura.ne.jp
That afternoon, what was silently placed on Seto's desk was a glossy pink-covered volume—one that was plainly out of place in a Kaiba Corporation office.
Seto frowned.
"Again. Where did you pick this up this time?"
Atem looked proud.
"This concept of manneri—it's fascinating. Apparently, when people have been together a long time, passion fades if they neglect to put in effort."
His tone was the same one the King used when deciphering complex inscriptions.
But what he held in his hands was a thick pink bridal magazine, its cover scattered with gleaming bridal gowns and smiling couples.
"…Where did you get that."
It was Seto's second time asking. The gravity had deepened.
Atem shrugged with a perfectly unbothered expression.
"The shop next to the cafeteria. This month's cover was cute."
Whether his standards for "cute" were still anchored in antiquity, or whether his aesthetic sense was simply its own thing entirely—Seto couldn't tell.
What he did know was this: the moment the word manneri was added to Atem's vocabulary, Seto's daily life would ripple once more.
Seto closed the magazine and exhaled, heavily.
No one suited the word manneri less than Atem. His habits, his thinking, even a single glance—nothing stayed the same.
Every morning brought a new idea. Every night, he came home carrying something stranger still.
Living with Atem, the feeling of ever getting used to him simply didn't exist.
"You—experiencing a rut…?"
Seto's voice was a tangle of exasperation and affection.
But Atem was serious.
"You can't let your guard down. Always be prepared. Even the best relationships can go dull over time."
If there were ever a day I had time to go dull with you, that would be a miracle. The words rose to Seto's throat—and were swallowed back down.
Saying it would only complicate things further.
Atem's research into manneri had begun.
Atem's phone buzzed.
The name on the screen: the editor from that pink magazine.
They'd become quite familiar lately.
"…Yeah. I have a moment."
When Atem picked up, Seto silently frowned.
A little while later, Atem looked at his phone with a mildly troubled expression.
"Seto. A question."
"I have nothing but bad feelings about this."
"The editor wants to know. How do we—as a quantum-married couple—deal with manneri?"
Seto went completely blank for exactly one beat.
"…What?"
A low sound escaped him.
"So I was wondering how I should answer—"
"You were going to answer?"
"I should respond sincerely, shouldn't I? I was asked."
Seto pressed his hand to his forehead.
This man—a king, and yet his curiosity and sense of responsibility operated well beyond normal limits.
Manneri.
There was no gap for something like that to slip into. None at all.
And yet Atem was genuinely preparing for it.
Seto exhaled quietly.
"…Before you answer that question, explain yourself. How much were you planning to tell them."
Atem said it with complete innocence.
"Everything."
Seto looked up at the ceiling.
The most manneri-proof existence in the world was, without question, Atem.
Atem settled onto the sofa and opened the pink magazine. Research into manneri.
The page corner was folded to the manneri special feature the editor had pointed out.
But as he read on, his brow began to crease, just slightly.
"Manneri… it really is difficult. What kind of state is this, exactly…"
Seto glanced over from his phone without lifting his head.
"It's exactly what it sounds like. 'Growing so used to something that the excitement disappears.'"
"The excitement… disappears?"
Atem looked at Seto.
In his eyes: a light of pure incomprehension.
Seto shrugged.
"An experience with no relevance to you."
That was simply the truth.
Every day, Atem surprised Seto, unsettled him, threw him off—just being beside him was enough to change the air in a room.
Manneri.
From where Seto stood, the word simply could not exist. That was all there was to it.
But Atem kept his expression serious, and something resolved in his gaze.
"Remaining ignorant is not acceptable. Knowledge is power."
Seto smiled, almost imperceptibly.
"That's very you."
A few hours later.
Atem had spread a notebook open on the desk and was writing in silence.
"What is manneri—
· Conversation decreases
· Losing interest in the other person
· Behavior becomes monotonous
· 'Excitement' fades…"
As Atem read each point aloud, Seto narrowed his eyes slightly.
"Every single one of those is maximally remote from you."
"Even so, I must study it. Preparation should be thorough."
Seto suppressed a laugh.
That very earnestness was the single greatest reason manneri could never touch them.
The next day.
Atem contacted the editor of the pink magazine, and somehow a short online meeting materialized.
"W-wait, you're doing a reverse interview… about manneri…?"
"Yes. I'd like you to teach me. What causes a couple to fall into manneri—and how does one avoid it?"
"Um… are you and your partner having trouble…?"
"We're not in trouble. But I want to be prepared."
"I—I see…! Well, let me think…"
Seto watched from across the room, and he could clearly see the editor on the other side of the screen going red in the face, struggling to find answers.
"…What are you doing, interrogating the editor like that."
Seto lowered his voice—equal parts exasperation and fondness.
Atem was perfectly serious.
"I'm simply collecting knowledge. Apparently manneri causes love to decelerate."
"…And your love is going to decelerate?"
Atem answered immediately.
"No."
At that flat certainty, Seto's breath stopped for just a moment.
Something deep in his chest quietly came undone.
"…Then there's nothing to worry about."
"I want to be prepared. For you."
The faint tremor in Seto's fingertips was detected, silently, only by A.R.E.S.
Atem closed the magazine and laced his fingers together in deep thought.
"…I wonder if understanding manneri requires actually experiencing it."
Seto set down his phone immediately.
"Hold on. You just said something outrageous."
"There are limits to imagination alone. A phenomenon can only be truly understood through reproduction."
He had the face of a pure researcher.
Seto put a hand to his forehead.
"…The moment you try to experience manneri, that very effort already places you as far from it as possible."
Atem nodded gravely.
"Which is exactly why I need your cooperation."
"I have no intention of cooperating."
At that moment, a message arrived from the editor.
"Atem-san, if you don't mind—I'd love to cover how you two spend your days as an example of couples who don't fall into manneri… honestly, a quantum-married couple would make the perfect feature!"
Seto moved to reply "Declined" immediately, but Atem quietly caught his arm.
"Seto, this is a learning opportunity."
On the other side of the screen, the editor pressed on with renewed momentum.
"If you're not experiencing manneri, you'd be the perfect example!
What do you talk about every day?
Any special arrangements in the bedroom?
How often do you argue?
Physical affection?
How do you express your love?
Our readers want to know everything!"
Seto lost his voice entirely.
A.R.E.S. dimmed the lights slightly—impossible to tell whether it was reading the room or not.
Atem tilted his head, chin in hand.
"…As I thought, I've never experienced manneri. Which means I need to identify the conditions required to reproduce it."
Seto tapped the desk lightly with one finger and said, quietly:
"Atem. The first condition is 'losing interest in the other person.'"
Atem answered at once.
"Impossible."
Seto's breath held—just briefly—and took on warmth.
"That exchange just now—can I use it in the article? 'Heat retention rates in quantum marriage' could be a whole new genre—!"
"You cannot."
"…It does have research value, doesn't it?"
"Don't take the editor's side."
"Please let us do a full interview next time!"
Seto exhaled and looked at Atem sidelong.
In his eyes: a certainty of feeling that no amount of commotion could shake.
"…Atem. Manneri will never touch you and me. Not in our lifetime. Researching it is a waste of time."
Atem smiled, softly.
"Even if it's a waste—if it's about you, I want to learn it."
Seto's pulse gave a small, quiet jump.
"Shall I raise the room temperature?"
A.R.E.S., ever attentive.
"Don't."
Atem sat before a mountain of magazines and research materials piled on the desk, reading through them with the same quiet focus he might bring to an ancient mystery.
A.R.E.S. reported discreetly.
"Atem-sama. The bridal magazine's editorial department has sent a message requesting 'a more detailed conversation.'"
"…Again."
Seto looked up from his documents.
"They just keep taking. The more sincerely you answer, the more that editorial team will…. Too late now, anyway."
But Atem didn't seem bothered.
If anything, he appeared to be enjoying what could only be described as a reverse approach from his research subject.
"Knowledge circulates. There's something to gain on our end as well."
Seto quietly knit his brows.
"…Be aware that that attitude is what keeps thickening their special features."
Atem carefully arranged the information he'd gathered, pulling out words like stagnation, habituation, and loss of novelty from the accounts of modern couples.
"…The causes appear varied on the surface, but at their root there seems to be one common property."
"Let's hear it."
Atem continued, in a serious voice:
"The absence of change."
Seto understood in a single blink.
"The source of boredom, then."
Atem nodded, and pushed his thinking further.
"The absence of change… a form that doesn't collapse, a ratio that stays stable, a structure without fluctuation…"
Seto felt a premonition of something unpleasant.
"Atem, don't finish that thought."
But Atem finished it.
"Isn't this close to the golden ratio?"
Seto's gaze went distant.
"Break yourself of the habit of explaining everything through the golden ratio."
"It's logical."
"It isn't."
But Seto had noticed.
That particular tendency of Atem's—it was nothing less than the instinct of a king who had spent millennia in pursuit of the ideal form.
The research Atem had so generously provided was being absorbed, just as generously, by the editor.
And a few days later:
Bridal Magazine Special Feature:
"Can Quantum Marriage Transcend Manneri?! The Secret Golden-Ratio Daily Life of This Power Couple—Fully Revealed"
The moment Seto saw the cover, he said, quietly:
"…As expected. Too late."
"It appears they calculated the 'rate of change' in your daily life and printed it as a feature."
"Don't print it."
"Can't be stopped now."
Atem picked up the magazine and turned the pages with the calm of someone reading a myth that had nothing to do with him.
"…Seto. Having our private life exposed—you're used to it by now, aren't you? Seikatsu-kan."
"Whose fault is that."
Atem laughed lightly and reached a hand to Seto's shoulder.
"If anything, it's useful. If the world is cooperating with the research, we get closer to understanding the true nature of manneri."
Seto exhaled slowly.
"Atem. All you're doing is trying to learn about the world—and the world makes a spectacle of your every move."
"Is that because I'm a king?"
"That's not all it is. …It's because it's you."
Atem's eyes shifted, quietly.
"Shall I raise the room temperature?"
A.R.E.S. was, as ever, attentive.
"Don't."
Atem had begun deliberately placing the golden ratio throughout every corner of their daily life.
The angle of the morning coffee mug. The fold of a towel. The way Seto's briefcase overlapped with his own documents.
"This should reproduce 'a daily life without change.'"
But A.R.E.S. reported:
"Atem-sama. The golden ratio of your daily life is within 0.01% of yesterday's. However, Seto-sama's movements are unpredictable, so reproducibility cannot be maintained."
"…And this is how you're trying to experience manneri?"
Atem nodded with an expression of complete seriousness.
"But I can't experience it at all. Why is that, Seto?"
Seto said it plainly.
"Your life is already at the golden ratio in its default state."
"To add: Seto-sama consistently registers Atem-sama's changes as 'stimulation.'"
"…So the reason I can't experience manneri is Seto?"
"Wrong. The cause lies with both of us."
"LOVE-OS analysis confirms."
Atem folded his arms and fell into thought like a scholar confronting an impossible problem.
"…It's supposed to be a phenomenon to avoid, and yet it simply won't visit us. Isn't that strange?"
"It's not strange. This is just what our relationship is."
The voice was remarkably quiet, and for just that moment, Atem almost forgot to breathe.
But Atem's research posture didn't change.
· Measure the rate of fluctuation in daily life
· Record the minute changes in Seto's expressions
· Have A.R.E.S. analyze the waveform of his own emotions
· Reconstruct the definition of the concept of tedium
"What is change… And what is happening inside me when I'm with Seto…"
And then he reached a conclusion.
"Seto is too new. This is no good for research."
"…You're part of the reason."
"I can't understand that."
"The reason Atem-sama cannot understand is that Atem-sama perceives Seto-sama as 'a being who is constantly being updated.'"
Seto gave a wry smile. Atem exhaled deeply.
"…Manneri really is difficult."
Around that time, the bridal magazine's editorial team was already drafting a new feature based on the information they'd taken.
"Beat the Rut! A Complete Feature on 'Time at Home'—as Taught by the Quantum-Married Couple"
The moment Seto opened the booklet, one word:
"…I don't recall giving permission."
"It appears they turned content 'shared for reference purposes' by both of you into an article."
"Don't use it for reference."
Atem stared at the page, head tilted.
"Seto. Why does our life keep becoming articles?"
"Because your explanations are too thorough."
"Research must be thorough."
"…Which is why the features keep multiplying."
Atem laughed quietly.
"Then next, let's research 'how to create change.' To avoid manneri."
Seto narrowed his eyes, just slightly.
"…I don't think that's necessary."
Atem's heart gave a small, bright skip.
A sigh from Atem fell into the night living room.
First button of his deep navy shirt undone, he turned slowly in front of the mirror.
"…Change really is a difficult thing."
The murmur was answered immediately, from behind him.
"The way you say it, it sounds like the founder of philosophy wrestling with an unsolvable problem."
Seto. Arms folded, watching Atem with eyes more exacting than any analytical instrument.
Atem lifted his chin.
"Even philosophers wrestle with this. Manneri is an abyss."
"No. You simply have no relationship with it."
Seto stepped forward smoothly, fingers sliding along Atem's collar.
"In the first place, for someone who looks like the golden ratio personified to research 'change'—"
"I did feel unsettled. I'll admit that."
"I thought as much."
Atem looked at Seto in the mirror.
Seto's expression was composed—but something warm stirred at the very bottom of his gaze.
"But I'm a researcher in my own right. To know the unknown, experience is necessary."
"What kind of man deliberately distorts the golden ratio just to experience a rut."
"The kind standing right here."
Seto laughed in the back of his throat. Low, and easy to listen to.
"…Atem, you've been too influenced by that magazine."
"The magazine's editor asked me how quantum marriage gets through manneri. But I had no answer to give."
Seto raised an eyebrow.
"Because you're not experiencing manneri in the first place."
"Which is exactly why I was troubled. Discussing a phenomenon I haven't experienced would be dishonest."
"Stop trying to be honest with the editorial department."
Atem shrugged.
"They put together good features. Even if they do take everything."
"That's not called 'coverage.' That's called exploitation."
Atem nodded seriously.
"Even so, they gave me a hint. Apparently 'manneri is an absence of change.'"
Seto said it flatly.
"At that point, it's something you'll never encounter for the rest of your life."
"Why?"
Seto ran his fingers through Atem's hair—and stopped.
Not straightening it. Accepting the change, as it was.
"There hasn't been a single day where looking at you felt settled."
Atem blinked.
Those words dropped heat, unexpectedly, somewhere deep in his chest.
"…Is that a compliment?"
"Obviously."
Seto took Atem's arm and drew him in, lightly.
"Besides, trying to change would be pointless."
"That's a harsh way to put it."
"The golden ratio cannot be moved."
Atem laughed in spite of himself.
"I see—treating me as a mathematical absolute. You might be the only one who does that."
"Clearly."
Atem let his voice drop, just slightly.
"…But when I told the editorial team we don't do anything for anniversaries, they were disappointed."
Seto answered without a pause.
"Anniversaries aren't necessary. You're a man who makes every day feel like one."
Atem's eyes went wide.
"Seto, that's…"
"Too romantic even for a romantic like you?"
"No. It's exactly like you."
Atem exhaled softly and leaned into Seto.
"I couldn't change."
"You didn't need to."
"…What about the me who tried to change?"
Seto's voice was, surprisingly, gentle.
"Adorable. Obviously."
Atem turned his face away at once.
"…That's the least manneri-adjacent line you've said all day."
"Don't worry. I can say it every day."
"Seto, that's not good. 'Absence of change' is manneri."
Seto tilted Atem's chin up, lightly, and said:
"The day I get tired of you will never come. No change required."
Atem surrendered with a slow exhale.
"…That's unbeatable."
"It was never even a contest."
They laughed together, just barely, and without either one deciding it, the distance between them closed.
The night that began with an attempt to break the golden ratio ended up doing nothing more than illuminating the unchanging, irreplaceable thing between them.
