An office late at night is, as a rule, honest.
Once the people leave, only the numbers flowing across the screens remain. Mio Himuro liked to watch those numbers. The hours when no one lied. Half the floor lights had been switched off, and only the hum of the servers carried up through the floor. Kotoba—the most-used social network in the country—and this place was something like its night-shift control room.
On the monitor in front of Mio, live ads streamed past by the thousands every second. To an ordinary eye it was nothing but a torrent of text and thumbnails. But Mio could see faces showing through at the bottom of it. This ad, right now, was reaching someone's phone. That someone would stop scrolling, stare at the screen, and believe it—she could see it all the way down to that person's profile, the image resolving whether she wanted it to or not.
At some point, someone at the company had started calling Mio "the Ice Bayes." Thomas Bayes was an eighteenth-century English minister and mathematician. Working backward from an observed result to the likelihood of the hidden cause behind it—he gave his name to that way of thinking, later known as "Bayes' theorem." The nickname gave the "ice" in Himuro to the namesake of probability, and it also caught the coldness of her profile as she peered into the depths of a sea of probabilities without mixing in a single drop of feeling. To Mio herself, it was neither a compliment nor a jab behind her back, just an accurate description.
That night, what floated up from the depths was the face of an older woman.
An ad bearing the photo of a famous investor. "Pick the stock I've chosen, and your money is guaranteed to grow." Mio did not process that one as just another ad. The face didn't belong to the investor. More precisely, it was the investor's own face, cut and pasted without permission. The copy had been boiled down to "guaranteed" and "limited time only," and at the end it tried to lure the reader out to an external chat. The domain it sent them to was three days old.
Each one, on its own, was a weak clue. None of them, alone, proved anything.
"Lies have a smell to them."
It was practically a murmur to herself. Mio's fingers touched the keys of her own laptop. Not Kotoba's production environment, but the personal code she had been chipping away at during her breaks.
A smell could be brought out with probability. Was the face really the person's? Did the wording have the shape of hype? Was the domain newborn? Bundle together clues that were weak on their own, multiply them, and "the probability that this is a scam" would rise up out of them. It was a way of thinking descended, from very far down the line, from the filters that bounce spam email.
The sounds of Mio's world receded, all at once.
In their place, only the depth of her vision stretched out, a thousand leagues into the distance. At the bottom of the torrent, weak clues glimmered here and there. The mismatched face. The hyped-up words. The newborn domain. Lights that pointed at nothing on their own—Mio tied them together with threads of probability and multiplied them. Points became lines, lines became a single road, and the road ran straight to where the lie was hiding. And at the end of it—a filter that would smoke out the scams took shape. Her clairvoyance reeled in the route to get there, one strand at a time.
"...Found it."
From there it was as if a dam had burst. The sound of keystrokes filled the empty floor. Mio's hands wired her personal detection engine into the production ad-delivery pipeline. Permission to touch production had been formally handed to her by her manager, Shiina, on the strength of her track record. It was an operation within what she was allowed to do. It was only the use she put it to that no one, probably, had seen coming. Anything with a scam probability above 0.95 would be dropped before it was displayed. That was all.
She got stuck once, at the seam. With the threshold set at 0.95, ads from legitimate brokerage firms got caught in the crossfire and dropped too. Without so much as a click of her tongue, Mio lowered the weight on face matching just slightly and shifted it over onto the hype. It wasn't perfect. Some things would still be dropped by mistake. Even so—if it meant one fewer person got deceived, tonight, at this very moment, then stopping them before they went out was more right than taking them down after.
Around the time the sky outside the window began, just barely, to pale.
Mio's fingers came to a sudden stop. On the last of the verification checks, green lights came on, one by one.
"...All green."
She sank into her chair and let out a short breath. The weapon was in production. From here on, it would do its job on its own.
And when the new week began, an inconvenient truth showed up in the form of a graph.
"Himuro. You're fired, effective immediately. Pack your things and never come back."
At the voice dropping down from the head of the table, Mio shrugged. She had no particular objection to the punishment itself. She had never had any attachment to a job or a title to begin with. The voice belonged to Sota Kiryu, fifty-five. The son of the late founder, and now the president of Kotoba. At the company, no one called the founder by name. They only ever said "the Founder."
More than the word fired, Mio's attention drifted to the monitor set on the long conference table.
The line graph of ad revenue had stepped down a stair from a certain point. The people who had been the marks of scams were quietly vanishing from the other side of the screen. However many vanished, that much revenue fell. The height of the step was exactly one tenth.
Mio traced the step with her finger. The meaning resolved into an image.
—One tenth of what this company earns...
A number that had been there all along; it was just that no one said it out loud. One tenth of Kotoba's revenue had been built on deceiving people. And her code had made it visible.
"Don't worry. That number will come back if you leave it alone."
Mio pointed to a corner of the monitor. The scam ads she should have been dropping until yesterday were beginning, one, then another, to slip through the mesh again.
"They're already moving. The same advertisers are swapping the face photos for someone else's, breaking up the phrasing of the hype, and replacing the domains they send people to with different, newborn ones. All on the very same night I put up one wall. Before long they'll slip past detection, and what was lost will come back."
A row of blank faces. Mio wasn't looking at them. The lost revenue no longer mattered to her at all. What had captured her was the speed of the other side, finding a gap in the wall in a single night.
Oddly enough, Mio felt no anger. Instead, a familiar sensation stroked its way up her spine.
"...This speed of response is unexpected. How interesting."
It was practically a murmur to herself. What Mio meant was the opponent who had come looking for a way over the wall overnight. But there were no ears in that conference room that could tell the difference.
"What's interesting about it?!"
Kiryu's voice cracked. He seemed to have taken her "How interesting" as insolence toward being fired. Only then did Mio notice that the man was angry. You noticed too late, Shiina's sigh across the table told her without words. Shiina—the one manager who had given Mio production access. The only man in the company who had properly assessed the skills of someone like Mio, who had neither credentials nor a title. She understood what that sigh meant, too. She understood it, and simply judged that, for now, it was low priority.
"You tampered with production without authorization and blew away a tenth of our earnings, do you understand?! And you call that interesting?!"
Kiryu was on his feet. It was the first time Mio had ever seen the man stand up.
"And what the hell are you, anyway? You never went to college, you never studied anything properly—you're just a little girl with nothing but a high school diploma! Why on earth does some high school graduate have access to our production environment?! It's absurd, it's beyond comprehension!"
Mio could not believe this man understood even a single line of how ad delivery worked. He was that kind of man: sitting in the chair of the company his father left him, believing the numbers his father built were his own achievement. He had no eye for judging who it was that could keep up, endlessly, with an opponent who changed shape and came over the wall again and again. All he had was the lost tenth and his trampled pride.
Academic credentials.
Mio filed the word in the noise folder. Credentials had nothing to do with what was happening right now—whether the production decision had been correct. Information that did not contribute to the point at issue was not processed. So Mio said nothing.
"Shiina! Did you give her that access?! That's a failure of supervision. You'll be demoted, mark my words!"
The point of attack swerved sideways. Shiina started to say something; his lips moved, but no sound came. This man must have his own reasons he couldn't speak of, too, Mio thought, detachedly. Perhaps he had some reason he couldn't defend his subordinate. Shiina lowered his eyes. That was all.
Mio pulled her personal laptop toward her and stood. She had no objection to the punishment. If there was one thing she would leave behind, it would be neither about credentials nor about revenue.
"—You need to put countermeasures back in place, quickly. The other side has already started on its next move."
Flatly. Not shouting, not accusing, just reading out the facts in front of her.
The words weren't aimed at Kiryu. The mind of someone who had just lost her job had already moved on to considering the next move. That was all it was.
Kiryu was still yelling something, but she was no longer listening. Tucking her laptop under her arm, Mio left the conference room. No one stopped her. Not even Shiina.
The only thing Mio took with her was her one personal laptop. What she had rewritten was the delivery logic. The code of the scam detection engine she had written for it stayed where it was, deep in Kotoba's servers, and slipped cleanly out of Mio's head. She had no habit of remembering things she didn't need.
Whose hands would one day dig it back up, and for what purpose—even her clairvoyance could not see that far, that day.
The elevator reached the ground floor. Beyond the automatic glass doors was the evening light. Mio was unemployed. No capital, no title, nowhere to go. And yet, strangely, her steps were light. Because she was still a little amused by that quick opponent—the one that came looking for a way over the wall the moment she put it up.
She walked out of the building, a few steps.
And a voice called out to her back.