Romantic Troubles of Duanmu-kun

Episode 18: The Mouse in the Box

A psychologist places a mouse in a box with a lever or button, designing the enclosure to eliminate all external stimuli. The box is configured so that when the mouse moves freely inside and performs the correct behavior, it receives food as a reward. Eventually, the mouse learns to use the button on its own.

Next comes the punishment phase. If the mouse demonstrates contradictory behavior, it receives punishment through electric shocks and water sprays. This similarly conditions the mouse to act according to human desires.

By repeatedly associating behaviors with rewards and punishments, one can cultivate specific behavioral patterns in the operator. By appropriately establishing connections between “rewards,” “punishments,” and “behaviors,” then releasing related “signals,” it becomes easy to manipulate an animal’s actions. This is known as “operant conditioning theory.”

The difference from traditional Pavlovian conditioning is that while the latter only modifies existing responses, operant conditioning generates new behavioral patterns.

For humans, this is a necessary step in animal domestication. For instance, these systematized behavioral research techniques are adopted when training racehorses or dogs for special missions.

Today, this seems like common sense, as modern education is based on these principles. However, in the past, theories that “human ability is determined by parental bloodline” promoting “eugenics” while neglecting education were once widely popular, so this wasn’t always the conventional wisdom.

But for some people, the value of behavioral control psychology isn’t limited to just training animals…

…

Miyagi Aki only truly connected the terms “signal,” “loud noise,” and “killer” after realizing the mastermind’s true identity. By then, she had already left Amazu Manor. However, she chose not to leave the Tokyo metropolitan area.

A train roared past on the tracks. Through the construction site barriers, she could only see a blurry white shape flash by. The sharp whistle reminded her of the emergency drill sirens from her distant school memories.

The sound tore through the air like ripping fabric, pouring into her ears.

“…This is the last location.”

She nodded repeatedly, showing no signs of disappointment. The train’s whistle gradually faded into the distance. At the final spot among fourteen target locations, they still hadn’t found any traces of the hidden killer.

…

Eight years ago, the most perplexing aspect of the serial killing case for the police was their inability to determine the perpetrator’s motive.

The killer hadn’t stolen anything from the victims, ruling out robbery. Additionally, there were no signs of sexual assault.

The victims shared no commonalities in age, gender, appearance, or occupation, and didn’t know each other. In other words, the killer had no particular grudge against them.

The only thing the victims had in common was that they were all killed through cruel methods. The perpetrator had no purpose or external drive, almost as if they were… “simply killing” for its own sake.

—But that wasn’t correct.

Back then, only young Aki understood the hidden “signal” in the series of murders.

It was the “loud noise.”

When faced with serial killings, people typically consider the killer’s characteristics through connections and similarities between victims.

For example, some killers might have been hurt by women in the past, leading to rape-murders or necrophilia; or they might collect organs due to their own disabilities… and so on.

But that conventional thinking was backwards from the start.

The Nagawa City killer wasn’t seeking something from the victims. Conversely, they were seeking victims for “something else.”

Whenever a specific “loud noise” occurred somewhere, a victim would appear nearby. Therefore, that person was killing based on sound signals.

Since no one would connect these two completely unrelated things, even if they noticed, they wouldn’t dwell on it.

Unable to find a rational explanation for this, Aki hadn’t mentioned it even when providing leads to the police.

What was the significance of seeking victims by following “sounds”? Was it due to psychological illness, some deeper reason, or simply killing out of boredom with an arbitrary criterion?

No one had ever made Aki so curious, to the point where she chose to investigate the truth of the incident herself.

But in the end, while she easily found the killer, she discovered they weren’t at all what she had imagined—though committing murder was an unforgivable crime and they were thoroughly despicable, there was still a fundamental difference in the degree of malice. That was why Aki’s attitude had changed eight years ago.

But now she understood and had the ability to get closer to the final truth. Since receiving those two emails from the “mysterious person,” Aki had developed new theories.

Otsuka Ken, who had escaped from the mental hospital, would likely find it difficult to threaten her—people’s abilities and personalities don’t change so easily.

So who could this person be?

Who else besides Aki and Otsuka Ken would know the procedure behind the Nagawa City serial killings?

If someone else had been involved from eight years ago—

A “mastermind” who had existed from the beginning but had never been noticed.

The reason for killing by following “sounds” was because it was a “signal” provided by someone.

A plan to make Otsuka Ken kill methodically, one after another, without needing to use easily traceable methods like phone calls or messages.

Someone was manipulating him from behind,

The real killer was like a pitiful mouse trapped in the psychologist’s box, without self-awareness or thought.

Just as in the last century, there were cases of using electroshock therapy to treat mental patients. In reality, it was just preventing people from thinking through forced suffering.

Because people are never satisfied with just manipulating animals.

Arbitrarily controlling their own kind is the ambition lurking in their hearts.

“Violence,” “sex,” “abuse,” “drugs,” “threats,” “electric shocks,” “Stockholm syndrome,” “brainwashing”…

It was entirely possible for people connected through the use of these various elements to achieve mind control to commit shocking crimes.

Even now, new religious groups and social organizations that seize benefits and satisfy organizers’ desires through such methods continue to operate in societies across countries. Aki, who had always observed “abnormal individuals,” knew this very well.

…

“So, which side is it?”

[TL Note: The title “箱中鼠” (The Mouse in the Box) is a metaphor comparing the killer to a lab mouse being manipulated through behavioral conditioning.]