Chapter Text
Disclaimer: Detective Conan is the property of Gosho Aoyama. I do not profit from writing this fanfiction. This story contains spoilers for Detective Conan and includes quotations from the manga, anime, wiki, and other sources.
When My Love Swears That He Is Made of Truth
Chapter I
Furuya Rei hadn’t thought much of Edogawa Conan the first time they met. The boy hadn’t made much of an impression—just another precocious child tagging along where he didn’t belong. That was why Rei had focused his efforts on buttering up Mouri Kogorou instead, going so far as to bribe the man in order to become his apprentice.
However, the more time he spent around Mouri, the more obvious it became: the man was nothing more than a mediocre detective—and that was putting it generously. There was none of the brilliance one would expect from someone with such a celebrated reputation.
Granted, for all his drunken antics and questionable behaviour, Mouri did have his moments. When a case struck close to home, he could be surprisingly sharp. He was also a skilled judoka—he had been the ace of the judo team during his time at Beika University—and an excellent marksman during his days with the police force. It was difficult to reconcile that past with the buffoonish man Rei saw today, but the evidence was there.
Still, none of that explained how Mouri continued to solve case after case with apparent ease. Eventually, Rei reached an unavoidable conclusion: someone had to be feeding him information.
And Mouri, with his inflated sense of importance and self-proclaimed detective prowess, never questioned it. He didn’t stop to ask himself how he’d suddenly become a genius overnight. He simply basked in the attention, oblivious to the true source of the deductions being credited to him.
And that, inevitably, shifted Rei’s attention to Conan—the boy who always seemed to be nearby whenever Mouri cracked a case. Gradually, piece by piece, Rei began to see the truth: it wasn’t Sleeping Kogorou doing the thinking. It was Edogawa Conan all along.
Vermouth had once questioned why he continued loitering around the Mouri Detective Agency, especially now that the Organisation’s business there was supposedly finished.
"But that business is over, isn't it?" Vermouth said. "Lucky coincidence allowed information on Sherry to fly into our hands... and we were able to send Sherry to her grave, after all."
"No, my interest has just suddenly been piqued..." he replied, "in the detective known as sleeping Kogorou that is."
And so he stayed at Café Poirot.
Officially, he remained on as the friendly, charismatic waiter—chatting with customers, serving coffee with practised ease, offering Mouri the occasional drink on the house. But in truth, he was watching. Specifically, he was observing the boy.
Furuya Rei was nothing if not thorough.
He watched. Observed. Analysed. The boy was always there. Quiet, unassuming, yet inexplicably present at every crime scene Mouri stumbled into. At first glance, Conan behaved like any other curious child. He tugged at Mouri’s coat, asked seemingly innocent questions, and wandered around crime scenes with that wide-eyed look children wore when pretending to be detectives.
But when Rei looked closer—really looked—he saw the precision in every movement. The sharp, calculating glint in those too-mature eyes.
Then there were the deductions themselves.
Rei had begun cross-referencing police reports from Mouri’s past cases—particularly the ones since Conan had come into the picture. The pattern was undeniable. Mouri's "brilliant insights" always followed moments when Conan had slipped away from the group. And more curiously, those insights often echoed things the boy had been heard muttering earlier.
Coincidence? Rei didn’t believe in those.
He’d also overheard Conan speaking to Inspector Megure once, steering the conversation like a seasoned investigator while pretending to be just a helpful child.
Of course, amidst everything else, Rei hadn’t forgotten about the so-called death of Akai Shuuichi.
From the very beginning, something about it had seemed off—too clean, too convenient. Rei was convinced the elusive FBI agent was still alive, and eventually, he was proven right.
But the cost of that knowledge was higher than he'd anticipated.
His cover had been blown—by none other than Edogawa Conan himself.
"Say, Amuro-niichan," the boy had said, far too casually for comfort, "you’re an enemy, aren’t you? Of the bad guys, I mean."
It was an innocent enough question on the surface. But Rei knew better.
That night, everything had unravelled. Every thread of deception, every shadowy assumption, had led to a single truth: Akai was alive. And the one responsible for orchestrating the entire elaborate charade was the child standing at the centre of it all.
Edogawa Conan.
The next morning, Conan had the nerve to call him a liar.
“You’re one to talk,” Rei shot back, eyes narrowing.
Conan simply smirked.
That infuriating little smirk.
There was no guilt in it, no fear—only the quiet confidence of someone who had already calculated every move five steps ahead.
Something had shifted after the truth came to light.
Before, Conan had kept his distance. Cautious, guarded—always watching Rei from the corner of his eye, as if expecting betrayal at any moment. But now, with the cards on the table and both of them knowing they stood on the same side, the boy had simply... let it go.
That, in itself, was unnerving.
It didn’t help that Conan was a terrible liar. His poker face cracked far too easily when Rei pressed him, and his attempts at feigning innocence were laughably transparent. But what unsettled Rei more was the way Conan carried himself when he wasn’t busy playing with the self-proclaimed 'Baker Street Irregulars'.
When the fun and games were over, he switched seamlessly into something else entirely. That bright-eyed façade slipped away, and in its place stood someone sharper, colder—older. A detective, yes, but something more than that. Something that shouldn’t have fit in the body of a primary school student.
Rei often found himself wondering how no one else saw it. How Mouri, Ran, Megure—how anyone—could look at Conan and not realise the truth staring them in the face.
He kept those thoughts to himself.
In the weeks that followed, Rei and Conan crossed paths on several cases. Sometimes by coincidence, sometimes not. They made an unnervingly effective pair—brutally efficient, almost wordless in their understanding. Their thoughts seemed to align without discussion, conclusions drawn from the same unspoken logic.
Rei was quietly stunned by how seamlessly they worked together. He wasn’t used to that—not even with his former colleagues. Conan was the only one who moved at the same pace. The only one who understood.
It was like chasing ghosts with a partner who'd already seen the crime unfold.
And sometimes... Rei wasn't sure if that reassured him—or scared him more.
Looking back, Rei had always excelled at whatever he set his mind to—academics, sport, martial arts, and everything in between. Efficiency came naturally to him. He was methodical, precise, and confident in his own ability to master any discipline he pursued.
But this time, he had met his match.
It was as though, in a sea of ordinary minds, they had recognised each other—equals in intellect, in wit, in their swift, barbed exchanges that flew over the heads of everyone else. There was a shared understanding between them that needed no explanation, a recognition that could only exist between two people used to living in the shadows of their own brilliance.
There was no denying it: Conan was a genius.
A mind that operated on a level beyond the reach of ordinary comprehension—beyond even Rei’s, at times. He wasn’t simply intelligent. He was extraordinary. The kind of intellect that didn’t just solve puzzles—it saw through them. Unwound them. Rebuilt them in an instant.
Rei was no stranger to prodigies. History was filled with individuals born ahead of their time—people whose abilities ignited admiration, awe, and no small amount of envy in those around them. People who pushed the boundaries of what humans were thought capable of.
But there had never been anyone quite like Conan.
Rei was burning with curiosity.
In the past, he had investigated the likes of Sherry and Akai Shuuichi. But now, his focus had shifted to an entirely different enigma: the curious case of Edogawa Conan.
As Bourbon, he specialised in deduction and intelligence gathering—skills he now applied with relentless precision. And with his real position in the Public Security Bureau, accessing official records was child’s play.
On paper, everything was immaculate. Legal documents, school registration, identification—all perfectly arranged, seamlessly slotted into the system. But Rei’s trained eyes caught the inconsistencies. They were expertly crafted fakes, certainly, but fakes nonetheless. To the average investigator, they would pass without question. But Rei was no ordinary man.
Conan had appeared from nowhere just over a year ago—suddenly attached to Mouri Kogorou’s detective agency, and from that point on, seemingly living under the same roof as Mouri and his daughter. There was no trace of him prior to that. No childhood photos, no nursery records, no medical history. Nothing real.
Further probing into his so-called parents yielded the same results. False names. Manufactured identities. Documents good enough to fool the banks, allowing them to open legitimate accounts to fund Conan’s daily life. But for Rei, the pattern was clear.
It was a ghost trail—one he’d seen before.
But why? No one simply sprouted into existence. And the ease with which Conan moved around the Mouri household—his casual familiarity with Ran, his knowledge of Kogorou’s habits—suggested far more than a year’s acquaintance. It implied history. Deep, personal history.
Fortunately for Rei, Conan had taken to appearing at Café Poirot more often these days.
In his quiet pursuit of truth, Rei began to spend more time with the boy—conversing casually over coffee and pastries, discussing ongoing cases and Sherlock Holmes novels. He even accompanied Conan on visits to bookshops and other places.
Conan had looked at him askance at first—confused, perhaps even suspicious. He’d narrowed his eyes, clearly trying to gauge Rei’s angle. But Rei had simply offered his usual charming smile and carried on, unbothered.
The truth was, Rei was playing a long game. But this time, it wasn’t for the sake of the Organisation, nor the Bureau.
It was for himself.
Because something about Edogawa Conan refused to add up. And Furuya Rei had never been able to resist a puzzle.
Those moments spent with Conan were, to Rei’s surprise, almost pleasant. Relaxing, even.
It was unexpected. As Furuya Rei, he wasn’t someone who sought emotional connection—he didn’t particularly like people. Not really. Once, long ago, he’d been hot-headed, impulsive, ruled more by fire than reason. But years of training had cooled that fire into cold discipline.
Still, there was something about those quiet, meandering conversations with Conan that unsettled him. And that, in itself, was dangerous. Because the questions hadn’t stopped. If anything, they’d grown louder.
Eventually, Rei gave in.
He took Conan’s fingerprints—subtly, carefully, a glass handled at the café, wiped clean before anyone noticed. It was a last resort. One he’d hesitated over, knowing it might confirm what his instincts already whispered.
When he ran them through the system, the result hit him like a punch to the chest.
Kudou Shinichi.
The fingerprints belonged to none other than the famed high school detective—the so-called Heisei Holmes. A sixteen-year-old prodigy who had mysteriously vanished from public life over a year ago… and now somehow existed in the form of a seven-year-old child named Edogawa Conan.
A brilliant teenager, reduced—no, compressed—into the body of a child. It defied logic. It flew in the face of science and common sense alike.
But the system didn’t lie.
And as the truth sank in, one quote from Sherlock Holmes surfaced in Rei’s mind, sharp and absolute: “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.”
It struck him like a revelation. No—like a reckoning. He sat back in his chair, staring at the result on his screen, his heart unnaturally still.
Kudou Shinichi hadn’t disappeared. He’d been hiding in plain sight all along.
There were now two circulating versions of Kudou Shinichi’s whereabouts.
The first claimed he’d been killed during an investigation—an unfortunate casualty of his own brilliance. The second, more widely accepted story, was that he had gone abroad to further his studies in the United States. That, apparently, was why his name no longer appeared on the student registry at Teitan High School.
Rei had overheard Mouri Ran and Suzuki Sonoko discussing the latter version. If that was what they believed, then it was likely the cover story Kudou had fed his friends to explain his absence.
And, truthfully, Conan being Kudou explained a great deal. His unnatural intelligence. His emotional restraint. His mature insight and calm under pressure. His seamless familiarity with the Mouri family. All of it made sense, now that Rei had connected the dots.
As for how it had happened… that had to be the Organisation’s doing.
Rei had once caught whispers—fragments of information passed between the highest echelons of the Organisation. Rumours of research into longevity, halting the ageing process, perhaps even reversing it altogether. Projects cloaked in secrecy, fringe science twisted into something far more dangerous.
Somehow, Kudou had got involved—and instead of dying, he’d been de-aged. Transformed into the child now known as Edogawa Conan.
Even the name was deliberate: Edogawa, from Edogawa Rampo, and Conan, from Arthur Conan Doyle.
Yet despite knowing the truth, Rei had no intention of exposing him. There was no advantage in it. Kudou, or rather Conan, was an ally in the long run. Useful. Brilliant. Dangerous only to those who required outmanoeuvring. For the present, Rei merely upheld the status quo—conversing with him as he ordinarily would, betraying no hint of what he knew.
Still, he must have slipped at some point.
Because Conan no longer bothered pretending in front of him. There was no fear, no caution. Only quiet acceptance.
Rei had seen it with his own eyes: Conan handling Professor Agasa’s gadgets out in the open, as if it were the most natural thing in the world. The voice-changing bowtie. The kick-enhancing shoes. The wristwatch torch. The transceiver badges. Tools of espionage disguised as toys—deployed without hesitation, even under Rei’s gaze.
It was maddening. And yet… intriguing.
Rei wasn’t quite sure when the line had blurred. But somewhere along the way, he had begun spending more time with Conan than necessary. More than protocol dictated. More than reason allowed.
And so, when he saw the announcement of a special Sherlock Holmes exhibition coming to Tokyo, he didn’t even hesitate.
He bought two tickets.
Conan was already there when Rei arrived at Café Poirot, tucked into his usual corner seat, eyes fixed on the pages of a well-worn book. A half-finished glass of orange juice rested beside it, beads of condensation clinging to the sides.
“Amuro-san,” Azusa greeted him brightly from behind the counter. “You’re in early today.”
“Amuro-niichan,” Conan echoed without looking up, clearly aware of his presence the moment he walked in. Rei caught a glimpse of the title on his book—The Sign of Four. Of course. Conan’s favourite.
“Conan-kun. Azusa-san,” Rei replied smoothly, loosening his scarf as he walked past. “The weather forecast said it might rain, so I thought I’d come in ahead of time.”
Azusa and Conan both turned instinctively toward the window. Sure enough, heavy clouds loomed across the sky, dark and sluggish, rolling in with quiet promise.
“Looks like you were right,” Azusa murmured, a faint crease between her brows. “Thank goodness the lunch rush is over—rain usually scares off the stragglers.”
Rei gave a noncommittal respond as he put on his apron.
"Ah Amuro-san, I just remember.” Azusa exclaimed suddenly. “Ogura-san said they're going to play baseball this Saturday. He asked if you want to join them."
“I’m sorry, Azusa-san, but I’ve already got something planned,” Rei declined politely, his tone as courteous and composed as ever—just as expected from Amuro Tooru.
“Oooh? Something planned?” Azusa leaned forward, eyes gleaming. “Don’t tell me—you’ve got a date! So, who’s the lucky girl?”
Rei offered a mild smile, not missing a beat. “Actually, I promised to take Conan-kun to the Sherlock Holmes exhibition this weekend.”
It had been meant as a surprise, but under the circumstances, he needed a plausible excuse.
“Sherlock Holmes?” Azusa blinked, then smiled. “So, you’re a fan too, Amuro-san. And here I thought you were going on a date,” she added teasingly.
From the corner of his eye, Rei noticed Conan looking up again—eyes glinting with quiet amusement, clearly enjoying every second of the farce. That smirk of his was infuriatingly smug.
Once Azusa disappeared into the back room to check the inventory, Rei walked over and slid into the seat opposite the boy.
“I see you weren’t exactly rushing to clear up the misunderstanding,” he said dryly.
Conan tilted his head, a picture of innocence. “But we are going on a date.”
There was mirth in his voice, yes—but something else too. Something that made Rei pause.
For the first time in as long as he could remember, his thoughts stuttered to a stop. It was like being punched by a hallucination.
“What?”
Conan’s smile widened, that familiar mischievous glint dancing in his eyes—the one Rei had come to associate with trouble, trickery, and calculated chaos.
“When two people like each other and spend time together, it’s called dating,” Conan said simply.
Rei blinked, utterly unprepared for the turn the conversation had taken. He opened his mouth—then closed it again.
Somewhere in the back room, Azusa called out something about running low on flour.
Rei barely heard her.
He stared across the table at the boy—at Kudou Shinichi, technically seventeen, physically seven, emotionally somewhere in between—and wondered, not for the first time, what on earth he’d gotten himself into.
Thinking back, all the time they’d spent together—the purposeful proximity, the shared smiles, the fleeting glances—it could be interpreted as something else entirely. It was hard to deny that now.
And if Rei was honest with himself, somewhere along the line he might have developed feelings for Shinichi. Shinichi—he couldn’t even think of him as Conan anymore. Not here. Not like this.
Shinichi, who was maddeningly brilliant, occasionally manipulative, endlessly surprising—and utterly bewitching. He would ruin him in rapture, Rei knew, if he wasn’t careful.
Unfortunately, he had already been careless. And now, sitting across from him with everything unsaid hanging in the air, Rei marvelled at how doomed he’d been from the very beginning.
Shinichi continued to watch him with quiet amusement, like a parent waiting for a child to put the final pieces of a puzzle together. The comparison should have annoyed him. It didn’t.
“Was it necessary to be so blunt?” Rei asked eventually, his voice dry but not unkind.
Shinichi raised an unimpressed eyebrow. “I thought it was obvious by now.”
Rei said nothing for a long moment. He just stared—intently, openly—as if seeing him for the first time. Now that the truth was out between them, bare and undeniable, it was impossible to look away.
Finally, Rei exhaled softly and spoke, a hint of exasperated fondness in his tone that he didn’t bother concealing. “I’ll pick you up on Saturday.”
Shinichi’s eyes lit up—sharp, keen, and unreasonably bright. "I'll be waiting, Zero no niichan," he said.
Rei’s traitorous mind wondered how anyone could have such a look directed at them and not fall wretchedly, desperately in love.
Author’s Note:
The title is taken from Shakespeare’s Sonnet 138: When my love swears that she is made of truth.