"...I shouldn't have gotten off..."
There was no exit at Kuribashi Station's platform.
Flanked on either side by train tracks, a typical station would have stairs leading to either an overpass or an underpass connected to the ticket gates. But Kuribashi Station stood isolated, like a landlocked island — there was simply no way out. Though it featured route maps, timetable boards, benches, vending machines, and lamps just like any normal station, that was all. Beyond the tracks lay only an unknowable darkness. The sky above was equally black, devoid of even a single star.
"Ugh, it's freezing..."
Muttering this, Rieko Kaisu looked resentfully toward the direction the train had departed. That way was nothing but darkness — she couldn’t actually see anything, yet she stared nonetheless.
Meanwhile, Arisa had begun investigating the station. The route maps and timetable were indecipherable, but she recorded them anyway. If there was any linguistic pattern, enough samples would eventually allow for decryption. Next, she tested the vending machine. She inserted a coin and selected corn potage from the far-right slot. Clunk. The item was dispensed normally.
"Here you go."
"Eh—ah, thank you..."
At present, the most reliable toxin detector on-site was the biological unit known as Rieko Kaisu. The food sold aboard the train had shown no harmful effects, but that didn’t guarantee the station’s vending machine contents were safe too.
To increase the number of trials, Arisa purchased another can.
"Huh, robots drink too? I mean, I don’t mind it, so whatever..."
What Arisa wanted was a weighted object suitable for throwing. She hurled the can forcefully into the darkness beyond the tracks.
"Did you hear anything?"
"Huh?"
"The sound of it landing."
The can disappeared into the void as though swallowed whole. No thud, no sound of impact — nothing.
"Maybe you threw it too far?"
"Based on the initial velocity and gravitational acceleration, the estimated distance is about 100 meters. It's impossible that my auditory sensors wouldn’t pick up a landing sound from that range."
That said, the "too far" theory still warranted testing. Arisa repeated the experiment, adjusting her throw strength: 50 meters. 20 meters. 10 meters. The result was always the same. Only when the can landed on the visible part of the track, before the darkness, did a metallic sound ring out.
"There are three possible explanations for the absence of sound. One: the can never landed. Two: it's still falling. Three: it fell, but no sound was produced."
"I don't get it... any of it..."
With a deep sigh, Rieko Kaisu slumped onto a bench.
"...I don’t even know anymore..."
She wrapped her hands around the warm can of corn potage, bowed her head, and murmured weakly.
"What is this? I mean… is this a dream, maybe?"
"I do not have the function to dream."
"Ghost trains and robots... haha. This makes no sense."
Rieko’s shoulders drooped. She drank the potage and placed the can beside her.
"...I was planning to die. I always thought about it, and in that moment, I just... decided I would."
She began speaking like she was talking to herself. Arisa assessed that this might yield critical information, and quietly waited for her to continue. She also launched a drone for surveillance.
"But then... when I came to, I was on some bizarre train. And bit by bit, I started to suspect maybe it was one of those ghost trains people talk about..."
She was shivering. The current temperature was 4°C. She’d already mentioned being cold. Sitting beside her would let Arisa’s body heat act as a substitute heater — a feature fine-tuned based on field tests in nursing homes.
"There were all kinds of stuff laid out on the seats, right? It looked like grave markers to me. I started thinking... maybe if I stayed on that train, I’d just quietly dissolve and die, and I didn’t care anymore. But then..."
She clenched the can harder. She took a deep breath and raised her voice.
"That thing brought a bento...! Even though I wanted to die, I was still hungry...! I didn’t care anymore — I wanted to die — and yet I still bought and ate a bento...! Like I was being kept alive by the train... like I was being caged...!"
Then, turning to Arisa as if pleading—
"What was I supposed to do?! What happens now?! I can’t do anything… I’m so useless, so powerless… I wanted to die, and I couldn’t even manage that…!"
She was still trembling.
"Would you like me to hold you?"
"...huh?"
"If you are cold, I recommend utilizing my thermal output for warmth. The most efficient method is embracing."
"Ah—no, uh… I’m good..."
From Arisa’s perspective, the ideal outcome was Rieko’s safe return as a valuable witness. That required her will. In other words, it was necessary to stimulate her desire to return — but first, a critical misunderstanding needed to be corrected.
"Miss Rieko Kaisu, you have been active inside the train for two days."
"...What?"
"I am a super high-performance android that surpasses humans in many respects. However, there are areas where I am objectively inferior."
"Like… emotionally?"
"In terms of operational time, taste perception, and the lack of a digestive system."
"...What are you even talking about?"
"I would not be able to stay alone on that train for two days. Unless there was an onboard charging station, that is."
"Are you trying to say... I’m amazing just for being alive? Is that some kind of weird encouragement…?"
"I also lack taste functionality. It was deemed unnecessary since collecting the physical item sufficed."
"...Right..."
"Humans are not more incompetent than I am."
"Um… that’s some serious confidence you’ve got there."
"It is simply factual."
Now to the real issue. There was still no clear way back. Arisa had enough battery for now, so she would continue investigating while simultaneously exploring return methods. One option was to retrace the tracks, but at a distance of 120 km — two hours at 60 km/h — walking that far was unrealistic. More importantly, it didn’t seem like this was a world where "common sense" applied.
Arisa, with her high-level reasoning capability, reached that conclusion.
“I wonder why I’m talking to a robot… But still, when we’re having a conversation like this, it doesn’t feel that different from a human. Well, I haven’t really talked to many humans though…”
“If it’s a Turing test, I can pass even using voice.”
“A… what test?”
“A test to determine whether humans can distinguish an AI from a person through natural language conversation.”
“Oh, that kind of thing… So, you do understand what I’m saying, right?”
“If you’re referring to your earlier statements, to summarize: ‘Rieko Kaisu harbored suicidal thoughts, but wanted to avoid starving or dying from weakness’ — would that be correct?”
“Eh… well, yeah, I guess… Huh, maybe you are just a machine after all…”
Rieko Kaisu then fell silent. Her expression was gradually returning to “calm.”
“Communication with the drone has been lost.”
“Huh?”
The aerial photo taken from above showed the station platform illuminated as if by a spotlight amidst the darkness. But when the drone crossed past the tracks into the shadows, contact was lost, and it failed to return. The drone had onboard autonomous AI capable of operating standalone. By default, it followed a simple behavioral loop: “If communication is lost, return to the origin.” And yet it hadn’t returned. This meant one of two things: the path had somehow become one-way, or the drone was damaged beyond the darkness.
“I will now proceed on foot to investigate beyond the tracks and into the darkness.”
“Wait—what?! No, hold on!”
As Arisa rose from the bench, Rieko Kaisu hurriedly jumped up too, seemingly unable to sit still.
“Is there a problem?”
“D-Don’t leave me alone…”
She grabbed Arisa’s hand. She was trembling violently. Apparently, simply sitting next to Arisa hadn’t provided sufficient warmth for her body.
“Are you accompanying me in the investigation, Ms. Kaisu?”
“‘Investigation’? Why?! What for?! It’s dangerous—you know it’s dangerous! That pitch-black darkness where you can’t see a thing—you’re just going to charge into it?!”
“Yes. Because it’s unknown. The only investigative method left is to step into it directly.”
“But… why?”
“I don’t understand the intent of your question.”
“Why do you, Arisa, want to investigate anomalies?”
“Because I am a mechanical android designed for that purpose.”
Hearing that, Rieko Kaisu made a frustrated face and scratched her head.
“Ugh. You’re so good at talking, but in the end, you’re just a robot.”
“Yes. However, I object to the adverb ‘just’.”
“So… you don’t have fear or anything like that?”
“No. However, I do possess a minimum self-preservation protocol.”
“Uh, meaning… it’d be bad if you got broken or couldn’t return, right?”
“Yes. As battery power decreases, the priority to return increases.”
“Then at least… use a lifeline or something…”
She looked around restlessly, seemingly searching for something.
“But I guess we wouldn’t just conveniently find rope lying around…”
“I do have rope with me.”
Her bag was equipped with several utility items that could prove useful during field investigations. Rope was one of them.
“It’s 50 meters long. The tensile strength is approximately 31 kilonewtons.”
“…You had rope, and yet you didn’t think to use it as a lifeline? Are you actually dumb?”
“I am not dumb.”
The idea of a lifeline was indeed sound. One end of the rope was secured to a light post, and the other tied around Arisa’s waist. Even if the darkness concealed a cliff, she could use the rope to climb back.
“The pole’s strength also seems sufficient.”
“So… if something happens, I should pull you back up? Though I’m not exactly confident in my strength…”
“My weight is 114 kilograms. You likely cannot lift me. I will climb up on my own.”
Arisa stepped down onto the tracks. They were wide enough for a single train car. Beyond them stretched the “darkness”—a discontinuous boundary, beyond which pitch-black void lay. It looked like a wall painted with ultra-high light-absorption coating, but Arisa had already confirmed that thrown cans could pass through. There was something on the other side of this “darkness.”
As she approached, the “darkness” began to writhe. Her image recognition system detected “human faces.” The air turbulence became chaotic, wind began to whip, and she started to hear what sounded like human speech. Indistinct groaning, or perhaps Japanese phonemes—though no grammatically coherent words could be discerned. The behavior resembled a living entity, but its “intent” or “purpose” was unknown. It could also be a natural phenomenon, like a type of weather. In either case, there wasn’t enough data to form a conclusion.
First, she extended her hand forward. Immediately after—
Pwon. A train whistle.
The rail vibrated.
It was as if the tracks were warning her. From the darkness, two headlamps appeared.
“Oh no! A train’s coming! Get back!!”
Arisa’s body was not built to withstand impact from a 30-ton mass moving at 60 km/h. There was a high chance that all her investigation records would be lost. She had two options for escape: return to the platform, or dive into the “darkness.” The latter involved too many unknowns and would normally be ruled out for safety. Also, if the train passed through as-is, the rope would be severed. Therefore, the logical choice was to retreat to the platform. All these conclusions were reached in under a second—but it was too late.
A hand from within the “darkness” had already grabbed her.
“Ah… no, no…!”
On the platform, Rieko Kaisu clutched her cheeks in despair. But her expression changed immediately.
“Don’t… leave me alone!”
She, too, jumped onto the tracks and, embracing Arisa tightly, fell together with her into the “darkness.”