When Atem offhandedly asks if Seto has any romance to speak of, Seto responds the only way he knows how — by turning it into a research project, with Atem as the test subject. What starts as a clinical experiment on whether love can override reason slowly stops being an experiment at all, for either of them.
This is a translation of an original work on Pixiv.
Original Title: 理性の崩壊試験
Original Author: 葉人(@Hathor₋yuki)
Personal site: https://prideshipping.sakura.ne.jp
"Kaiba, don't you have even one or two romance stories by now?"
The moment the words left his mouth, Atem's face showed the look of a man who suspected he'd just pressed some irreversible switch.
Understandable. The man across from him was someone who trusted logic over love.
"Pointless."
Seto said it without even lifting his eyes from the display.
"If I had spare time for something like that, I'd invest it in something more efficient. Do you know what the single greatest factor that derails human behavior is? Emotion."
"...Well, that's true, but."
Atem faltered slightly, but kept his joking smile in place.
"But a life without feeling sounds pretty flavorless. Even you, someday..."
"The analysis simply hasn't been done yet."
Seto stood, cutting the words off cleanly.
His eyes were those of a scientist who'd just found his research subject.
"At what stage does love erode reason, and to what degree does it affect behavior. If that can be quantified, this 'pointless phenomenon' could be proven."
"So you want to quantify the relationship between love and reason. ...Are you planning some kind of experiment?"
"Starting immediately. Right here."
Atem's smile stiffened.
He asked, his voice mixed with curiosity and wariness.
"...And the subject?"
"Don't make me say it."
Seto's lips curved faintly.
There was already, in that smile, some sign that the edge of his own reason had begun to fray.
Seto explained the whole thing as if laying out a research plan at a laboratory.
Calm, perfectly logical, with no trace of feeling in it at all — or so it seemed.
"But to confirm it with an 'experiment'..."
"Who was it who brought it up? 'Don't you have even one romance story by now.'"
"Normally, no one expects that to actually become a research topic."
"You said it. Take responsibility for it."
Atem frowned slightly and looked away.
The light of the afterlife fell softly across his profile, and Seto watched, wordless.
Silence.
A beat slightly too long, the kind that makes you hold your breath.
"The subject will cooperate."
At that line, Atem's shoulder twitched.
"...So it is me, isn't it."
"Obviously."
Seto crossed his arms, a faint smile touching his mouth.
An expression that could pass for provocation.
That composure alone was enough to shake Atem's reason.
"Kaiba, that's hardly a fair experiment..."
"If fairness concerns you, feel free to refuse."
"...!"
"But given that you were the one who joked about 'romance stories,' backing out now would be a defeat."
A voice, quiet but sure, drawing him in.
The sensation of being caught, little by little, in a net of words.
Atem held his breath without meaning to.
"My aim is one thing. Whether love breaks down reason."
Seto's blue eyes fixed on Atem as if piercing straight through him.
"At that boundary, I'll observe how you change."
"...Observe?"
"I'll record the results of the exchange."
There was no sweetness in that tone, no warmth at all.
And yet, precisely because of that composure, something stirred uneasily in Atem's chest.
"Is this really only for the sake of the experiment?"
"For now."
"For now?"
"It depends on the results."
Seto took a step closer.
Close enough that their breath would nearly touch.
The instant Atem's throat moved, Seto let the words drop.
"Once the critical threshold of affection is crossed, this stops being an experiment."
Atem had nothing to say.
The test of reason was supposed to be on him — but it was he himself who was being tested.
He understood better than anyone that he was already being made to dance in this man's palm.
A few weeks after the "exchange" began.
Atem sank into the back of his chair, gaze turned away.
He was aware of his own breath growing shallow.
"...Letting emotion tangle up your 'experiment' is dangerous."
"Confirming that is the entire point."
Seto's answer came instantly.
As if he'd already anticipated exactly this reaction.
"The subject either raises an objection, or falls silent."
Seto opened his notebook, unhurried, and wrote something down.
The pressure of the pen was steady. Flat, composed.
But to Atem's ears, the scratch of that pen against paper carried a strange heat.
"...What did you just write?"
"'Initial resistance response: voice trembling, gaze avoidance.'"
"Even if you call it an experiment, you could at least..."
"'Faint emotional waver in tone. Prioritizing self-restraint.'"
"Stop it!"
The instant his voice rose, Seto's mouth lifted slightly at the corner.
Not a provocative smile — the calm delight of an observer.
"Interesting. The pupillary response, at the moment of resistance... clearly dilated."
"...."
"Your reason is already being interfered with."
Atem started to rise, then stayed where he was.
Running would be easy.
But running meant losing. He understood that logic better than anyone.
Turning his back on a fight simply wasn't in his nature.
"...Keep going. Observation, or whatever you want to call it."
"Unexpected. That you'd accept a critical-threshold experiment yourself."
"I have no intention of losing to your provocation."
"Oh?"
Seto set down his pen and walked slowly toward Atem.
Point-blank range.
He reached out, straight for Atem's cheek.
His shoulder jumped, reflexively.
Seto confirmed that tremor with his fingertips, murmuring.
"'Autonomic nervous response to tactile stimulus: clear tension.'"
"...If you're going to observe, at least keep your distance."
"I haven't collected data on closing the distance yet."
Atem lowered his eyes.
His own heartbeat was fast.
Not anger, not agitation — something else, some other heat entirely.
Seto's expression clouded, just slightly.
Even as he tried to remain the observer, something stirred faintly in his own chest.
He was supposed to be watching the moment reason collapsed.
Their gazes crossed.
One second. Two.
The silence sank deep.
Atem let out a small breath.
"Kaiba... you should record this too. 'Observer's pulse: elevated.'"
After a moment's silence, Seto let out a small laugh.
"...Interesting. So you're both the experimental subject and an observer yourself."
"Whoever loses their reason first. That should be part of the experiment too, shouldn't it."
"Hmph. Fine. But be warned. Before I cross my own threshold, you'll be the one to break first."
Seto closed his notebook again and set it down slowly on the desk.
A small sound echoed.
It seemed to signal the beginning of the experiment's "second phase."
Several more weeks had passed.
In the silence, Seto's pen stopped mid-motion.
Until a moment ago, every word on the page had been figures and records.
But now, his hand had stilled.
Something was wrong.
At the far end of the gaze meant to observe the subject, composure refused to return.
Atem sat quietly, leaning back in his chair.
His posture hadn't changed, and yet he looked, somehow, softer.
Was it the quality of the light, or a trick of the eye.
Or perhaps, some distortion born of the observer's own feelings.
Seto drew a breath at the corner of his mouth and tried to steady himself.
"...Pupillary dilation, mild but sustained. Heart rate... also still elevated."
"You're recording that after your hand touched me."
"You think that's the cause?"
"Can you deny it?"
Atem laughed softly and looked away.
"Maybe it's my reason that isn't functioning right now... but as the test subject, I suppose I should take that seriously."
"That, too, is part of what's being observed. The rate of emotional erosion is within expected parameters."
"Expected?"
"Who do you think I am. This outcome, for you, is only natural."
Seto's voice stayed flat.
But in the way he said "natural," there was a faint waver.
Atem didn't miss it.
"...You're a little different too."
"What is."
"The way you touch me is gentler. The temperature of your words has changed."
"I've only adjusted the angle of observation."
"Is that really all it is?"
Atem's eyes fixed straight on Seto.
Somewhere behind the mask of the cold scientist, something creaked, quietly.
Seto picked up his pen again. But what went onto the page wasn't a record.
Observer's response: observational accuracy destabilizes in moments of perceiving the subject as beautiful.
For an instant, his vision blurred.
It was his own heart rate that had risen. Absurd. This was an experiment.
Atem stood quietly and approached Seto's desk.
Close enough for their eyes to meet directly.
At that distance, Atem murmured.
"Is this what observation looks like?"
His hand touched Seto's cheek.
This time, it was Seto's shoulder that trembled, faintly.
"...Aren't you going to record it?"
"There's no way I can write this down."
"Why not."
"Because I've become the subject."
Atem smiled faintly.
That smile carried a quiet heat, the kind that seemed to melt reason itself.
"Was that within your expectations too?"
"...No. This is a miscalculation."
Seto's voice was low, faintly rough.
Those words became the signal marking the end of the experiment, and the beginning of something else entirely.
The scratch of paper-on-pen had gone quiet in the room.
In its place: faint breathing, the quiet sense of thought turning over.
Seto tapped the desk with the end of his pen, trying to put his own state into numbers.
Heart rate, speed of thought, clarity of memory.
Every one of them showed an anomaly.
Since contact with the subject, his emotional response hadn't settled.
Merely seeing the subject's figure was enough to overstimulate the reward system.
However many times he turned it over, it was, unmistakably, romantic feeling.
Seto knit his brow and let out a deep breath.
"Don't tell me. Me."
The words, murmured without any humor, fell into the room.
Meanwhile, Atem sat in the chair across from him, arms crossed.
He was thinking quietly, as if looking into his own chest.
The resistance was already gone.
If anything, there was a sense of being filled, simply from the sight of Seto.
"...Same here."
He murmured it to no one in particular.
What remained, at the end of all that thought, was a single word.
I like you.
After another silence, Seto stood.
He set down the pen he'd been holding.
Atem's eyes followed the motion naturally.
"I've reached a conclusion."
"Go on, then. Let's hear it."
"As a result of the experiment, I've confirmed romantic feelings toward the subject."
Atem's eyes widened.
"...Meaning?"
"Treating the subject as a partner is the most natural course of action."
A flat voice.
Words far too composed for the moment.
But there wasn't a trace of joking or evasion in them.
Atem's mouth lifted slightly at the corner.
"So this is what a scientific confession tastes like. Pretty dry."
"Feelings can't always be explained by logic. But this is my own kind of sincerity."
"...I see. That's very you."
Atem stood too, slowly, and walked up to Seto.
"I agree with the conclusion. Let's redefine the relationship between observer and subject — as partners."
Seto's eyes narrowed slightly.
"Redefine, huh. If that's what you want to call it, I won't argue."
A small pause fell between them.
Something soft filled that empty space.
Atem voiced one last, small complaint.
"Though... I'll admit, I would've liked at least one plain 'I like you.'"
Seto drew a quiet breath, and said it, low.
"I love you. No other vocabulary is necessary."
Atem lost his words, and smiled.
The point where logic and feeling finally met — that was their "critical threshold of love."
Atem fell silent for a moment.
What broke that silence was a voice, faintly embarrassed, but straightforward.
"...I love you too."
Seto raised an eyebrow.
But the words that followed carried a touch of wry amusement.
"Still, this feels like a research presentation. We're both saying 'I love you,' and it's not the least bit romantic."
The corner of Seto's mouth moved slightly.
"Because logic keeps winning out?"
"I won't deny it."
"Then let me apply a correction."
With that, Seto pulled Atem's waist toward him without warning.
Atem caught his breath at the sudden move, and Seto traced his cheek with a fingertip, slowly bringing their lips together.
Once, twice.
Leaving theory and words behind, as if simply confirming something real.
Even after their lips parted, almost no distance remained between them.
Seto's voice was low, faintly rough.
"That should be more than enough romance for you."
Atem flushed and looked away.
"...Unexpected."
"Not even reason can beat you."
"That's supposed to be my line..."
Seto laughed.
Calm, but with a certain triumphant edge to it.
Seeing that expression, Atem let his shoulders drop, as if sighing.
"I really do feel like I'm being made to dance in your palm."
"If you're going to dance, that's more than enough."
A gentle silence returned.
Only their touching hands still recorded each other's warmth.
Seto murmured, quiet, at last.
"A phenomenon logic can't explain... Is love a phenomenon with no reproducibility at all?"
Atem laughed softly.
"So it's a miracle, then? I don't mind, if it's a miracle. I'm sharing it with you."
Seto squeezed his hand back.
"I suppose I'll write this into the next paper. Experiment successful — love does exist."
Atem laughed, exasperated, and let his head fall against Seto's chest.
In the quiet night, only a happiness beyond logic sank slowly into place.
The night had already begun dissolving into the pale first light.
At the desk, the thick research notebook still open, Seto ran his pen across the final page.
Subject: A
Condition: emotional shift confirmed.
Result: through mutual interaction, the critical threshold of reason was surpassed.
Conclusion: subject = partner.
He finished writing in his smooth, even hand, and the tip of the pen paused for a moment.
His own handwriting looked, somehow, unusually gentle.
"That'll do."
The instant he murmured it, Atem's fingers reached from behind and took the pen.
Pulling the notebook toward himself, he added a line of his own, easily.
Research concluded. Changed to a joint study, at the subject's own will.
And then, carefully, he signed it.
Atem.
Seto's mouth lifted at the corner.
"Adding to it without permission, I see."
"A co-researcher's right."
"So, what's the research theme going forward?"
"'The reproducibility of love.'"
Seto laughed lightly.
"If the same phenomenon can be reproduced, I'll run the experiment every night."
Atem nodded, deliberately keeping a straight face.
"A highly reproducible study is worth trusting. ...But that's enough for tonight."
Seto laid his fingers over Atem's hand, still resting on the pen.
The instant their fingertips touched, Seto murmured, low.
"A signal marking the end of the experiment ought to go in the data too."
The light touch of their lips wasn't a research report — just proof of happiness, plain and simple.
The notebook on the desk stirred faintly in the breeze.
On the final page, beneath Atem's signature, Seto's handwriting appeared as well.
S. Kaiba
Reproduction successful.
