Dawn came, but morning never entered the building. The light that filtered through the broken windows hung suspended in the air—a pale, floating thing—mixing with dust and mold and something far older that had settled into the abandoned space. Sōyō Yūichi had been staring at the laptop screen spread across the reception counter for more than two hours already. The frequency graph glowed softly in the darkness. Three recordings from last night. Of those, the most significant one—the audio pattern detected from the direction of the second-floor corridor—had been rendered into a graph with frequency on the horizontal axis and amplitude on the vertical. The problem area was below 20Hz. Infrasound, the band human ears supposedly cannot perceive. Yet there, unmistakably, was a peak. Yūichi's fingers touched the neck strap holding his equipment. The weight of the machinery transmitted itself to his shoulders, as it always did. The shape of that peak matched the resonance characteristics of the human vocal cords. He couldn't be certain. There was only one data point. But that single point's shape was quietly shaking the judgment his experience had accumulated. One hundred twenty-seven cases. By the time he'd arrived here for the one hundred twenty-eighth, every record he'd gathered knew this shape. (This is not normal.) Before he could fully form the thought into language, an engine sound came from far away. A low, steady four-wheel-drive engine climbing the hill. Yūichi lifted his eyes from the screen and looked out through the broken window. Mist still lingered. The white haze that had settled into the valley of Kirisuke Town was slowly thinning in the morning light. The engine sound drew closer. Tires crunched on gravel in front of the entrance. The engine cut off. A door opened. Shoes pressed into sand. A single beat of silence— "This building has three vertical cracks on the south exterior wall. Spalling confirmed at the corner facing the parking area. Two locations on the first-floor window frames show exposed rebar. Structural priority inspection is necessary before deciding on the equipment transport route." That was Nanjō Reina's first words. Not a greeting. Not small talk about the weather, not an initial impression of the abandoned hospital, not anything of that kind. Building condition, safety risks, equipment transport priorities—everything came out in the language of practical work from the moment she arrived. Yūichi stood and walked toward the entrance hall. Nanjō Reina stood just inside the doorway. Twenty-seven years old. One hundred sixty-two centimeters tall. Her bright reddish-purple bob cut shifted subtly in the morning light, changing color as it caught the rays. Emerald-green eyes were already assessing the condition of the ceiling panels. A small tattoo at her left temple flickered in and out of sight with each movement of her head, depending on how the light fell. In her right hand, a pen-shaped tool was wedged—a portable hardness tester for building materials. That was the kind of person who understood all of this within three seconds of meeting, Yūichi thought. The intuition cultivated over one hundred twenty-seven investigations performed an almost unconscious assessment of the person before him. This human did not let emotion guide her work. And she was the type of specialist who increased precision by eliminating emotion entirely. "Nanjō." "Sōyō. I reviewed the report beforehand. For a reinforced concrete structure built in 1982 that's been abandoned for fifteen years in a humid inland mountain environment, the carbonation depth could have reached thirty to forty millimeters. Concrete carbonation is a deterioration phenomenon where carbon dioxide in the air causes the concrete to lose its alkalinity, making the internal rebar more susceptible to rust. Before going up to the second floor or higher, let me confirm the main columns and beams." Yūichi nodded. "Understood. But before that, I'd like to share the recording data from last night. It would be better to check it before we proceed." Reina's gaze turned toward Yūichi directly for the first time. ――― The restaurant "Yamakasumi"—a narrow eatery with just a counter and two four-person tables, facing the shopping street in the center of Kirisuke Town—hung out its noren curtain starting at seven in the morning. When Sōyō Yūichi and Nanjō Reina entered, there were no other customers. The proprietor, Sakuma Toshiko, paused for just a moment when she saw them. Yūichi had come the day before. And today he was with someone else. She said nothing, but her eyes registered that the number of people heading toward the old Lapis was increasing. The miso soup from the set meal was brought to the table. Tofu and green onion. The scent of dashi carried with it a temperature from an entirely different world than the air of the ruins. Yūichi opened his notebook and breathed in that aroma for a few seconds. "Listen to this." He opened the laptop and turned it toward Reina. He inserted the earbuds. Pressed play. Reina went still. Yūichi couldn't hear what was coming through the earbuds pressed against her ears. But Reina's expression—the expression that had been stable as a measuring instrument until that moment—shifted. Only slightly. Truly only slightly. Not a furrow between her brows. Her eyes' focus had fixed on a single point. The shape of concentration, the form of someone seriously processing something. Thirty seconds passed. "There's a possibility of building resonance specific to abandoned structures." Reina spoke without removing the earbuds. Her tone was concise and clear. "When a building undergoes micro-vibrations from temperature differences or wind pressure, specific frequencies can be amplified. Residual vibration in piping is also a candidate. I haven't confirmed yet how much of the boiler system piping remains in this building. And then there's the wind tunnel effect from the mountain terrain—air currents moving from the valley toward the hilltop could resonate with the building's structural elements." Three possibilities. Immediately. All three hypotheses that Yūichi had considered before recording last night came out in exactly the same order. "All of those have been ruled out." Yūichi displayed the graph. "Building resonance can be excluded based on the frequency characteristics. Structural resonance in abandoned buildings typically occurs along the building's natural frequency, but the peak in this data doesn't match that band. Regarding residual vibration in piping—during last night's observation, I ran a temperature data logger and electromagnetic field meter simultaneously. The same pattern was recorded during time periods when the conditions for vibration—thermal expansion and contraction from temperature differences—were not occurring. As for the wind tunnel effect, when I cross-referenced the observation data with meteorological records, it doesn't align with the time periods when wind speed was below 0.3 meters per second." Reina looked at the graph. For a while, she said nothing. Yūichi waited. There was no need to rush her. The data wouldn't change. He could simply wait for Reina's thoughts to reach their destination. Reina's finger touched the trackpad and enlarged the graph. The region below 20Hz. The shape of the problematic peak. Her eyes carefully traced its contours. Eventually, Reina removed the earbuds and set them on the table. She said nothing. No affirmation, no denial, no interpretation—nothing came out. She simply stood, looked out the window at the morning of Kirisuke Town for one second, then returned and drank her miso soup. That silence was enough for Yūichi. A person who receives data honestly wears that expression. Before facts that cannot be refuted, they say nothing unnecessary. That stillness was not denial. It was the form of acceptance. On the mountain road driving back to the old Lapis, Reina spoke while looking out through the windshield. "Completed in 1982, reinforced concrete construction, three stories plus one basement level. Any renovation records?" "According to official records, exterior wall repairs once in 1995. Nothing after that." Reina gazed at the cedar forest outside the window for a while. "In a humid inland mountain environment, at an elevation of five hundred forty meters, assuming thirty to fifty freeze-thaw cycles per year in winter, the exterior wall cracks are progressing at the expected rate. The records indicate the basement is only a mechanical room, but if the area reaches forty percent of the first-floor footprint, the ventilation design must be unusual. Depending on the actual ventilation pathway, there's a possibility the structure creates an upward air current from the basement to the first floor." Yūichi carved those words into his memory as he navigated the unpaved road's curves. The basement. Ventilation pathways. The direction from which the strongest response came in last night's recording—it aligned with the direction toward the basement. Yūichi already knew this fact, but he quietly confirmed the weight of those words coming from someone with architectural expertise pointing to the same location. He had known since last night that he couldn't accurately judge dangers outside his specialty. What he'd cultivated over one hundred twenty-eight investigations was experience in acoustics and electromagnetic fields. Whether a building's structure was safe, where the risks of collapse lay—that required different expertise. That expertise was now sitting in the passenger seat. It was a condition that fundamentally changed this investigation. ――― The closed psychiatric ward on the second floor was quieter than he'd imagined. All the fluorescent lights in the corridor had been destroyed, and some ceiling panels had fallen away. White fragments scattered across the floor, making dry sounds with each step. Reina walked ahead of Yūichi, confirming the boundary between walls and ceiling with her flashlight. She tapped key points with the pen-shaped tool, determining the internal condition from the quality of the sound. Knock, knock—a regular rhythm echoed through the corridor. The nurse's station was in the middle of the corridor. The counter's glass was shattered, scattered across the floor. The file storage shelves inside remained half-open. Yūichi entered first. He illuminated the interior of the shelves with his flashlight. Old documents, binders, bundles of medical records—most were bound together by moisture and covered in mold. But as he carefully examined what was within reach, his finger stopped. A patient admission ledger. The cover read "Admission/Discharge Records 2006—2009." He opened it. Serial numbers were printed throughout. P-001, P-002, P-003—the numbers progressed with each page turn. Yūichi traced the sequence with his finger, confirming each one. P-047, P-048—here it jumped. The next page was P-057. Nine records were missing. He continued. P-071 was followed by P-079. Eight records were missing. Yūichi brought the binder to the window and examined the binding holes in natural light. The pages had been torn out. Fine paper fibers remained along the edges of the holes. If they'd been shredded, no such traces would remain. This was the mark of pages being pulled out by hand. Moreover—Yūichi examined the angle of the torn edge—the fracture surface was uneven. They hadn't been removed one by one carefully, but rather in bunches, hastily, all at once. He checked the classification tabs as well. The labels on the shelf dividers showed clear discontinuity in the numbering. The divider that had held the label for P-049 through P-056 remained empty. "Nanjō." At his subdued call, Reina came in from the corridor. Yūichi silently showed her the torn pages and illuminated the label discontinuity with his flashlight. Reina crouched down and examined