Mira had spread out on the translation desk what appeared to be a descent route map—dozens of sheets of paper joined together and hand-drawn. A cross-section of Luminaire Deep was depicted. Down, down, down from the Sacred Archive. The distribution of phosphorescent moss, temperature fluctuations, known danger zones—all written in fine script. Elara found herself absorbed in it for a moment. (This is incredible. Did she make this alone?) However, from a certain point onward, things looked different. "From here, it says 'estimated,'" Elara said. "That's correct," Mira replied. Mira answered quietly, but clearly. Her silver-braided hair hung over her shoulders, and the phosphorescent ore ornament swayed gently as it caught the archive's pale blue light. "I have never descended beyond that point. It is a range estimated from manuscript descriptions and topographical data," Mira said. Elara stared at the blank portion of the paper. Below the word "estimated," the outline of terrain continued, drawn in faint pencil. Lines without certainty. But Mira had said that beyond that lay the remains of the Spinthread Corridor. Palimpsest civilization—an ancient super-civilization erased from all dimensions roughly twelve hundred years ago—its ruins. "When cross-referencing the descriptions in the seventeenth and twenty-fourth volumes of the manuscripts, the descent to the arch structure at the deepest level requires approximately three hundred meters in vertical distance from the archive. However, accounting for terrain distortion, the actual route would be—" Mira said. "Wait a moment," Elara said. Elara raised her hand. Mira's gaze turned toward her. "The seventeenth volume is the one that records air current fluctuations in Luminaire Deep's deepest regions, right? A resource including wind direction, speed, and seasonal variations. And the twenty-fourth volume—the one recording the habitat of Lumina Swarms. Lumina Swarms are small beetle colonies that inhabit Luminaire Deep, and when they number in the thousands, they bundle the weak electricity of individual organisms to generate bioelectric currents that paralyze prey—but when you cross-reference those two, the air current pathways and habitats might overlap, which means the safety premise of the descent route—" Elara said. "Exactly," Mira said. There was a slight heat in Mira's voice. She was speaking a bit faster than her usual quiet tone. "When overlaying the habitat data from the twenty-fourth volume with the air current map from the seventeenth, the eastern route becomes something to avoid. Since Lumina Swarms have the habit of traveling on air currents, the risk of encounter is dramatically higher on the eastern side where currents concentrate. That's why I've set the western detour as the estimated route, but when you add the extra distance from the detour, the actual—" Mira said. "In other words," Kael said. Both fell silent at once. Kael, leaning against the wall with his arms crossed, had opened his mouth. His short hair, dark navy with red mesh, was tousled as usual. His amber eyes moved back and forth between the map and the two of them. "The map ends partway through," Kael said. There was a pause. "That's not what we're saying," Elara and Mira said in unison. Their voices overlapped. Kael shrugged. A dimple appeared, then faded quickly. "Fine, fine. Tell me the details on the way down," Kael said. —— Elara watched from a distance as Mira locked the archive door. It was an old iron lock. Mira's slender fingers turned the key with practiced ease. A hard click was absorbed into the cavern air. "You don't lock it often?" Elara asked. "There's usually no need," Mira replied. As she tucked the key into her coat's inner pocket, Mira gazed somewhere distant. "Leaving this archive is... perhaps the first time since my childhood," Mira said. Her tone of voice hadn't changed. But the weight of those words made Elara's feet stop. Since childhood. The first time. Alone in this vast archive. Surrounded by the world of manuscripts. Elara looked at the archive entrance. Stone walls illuminated by pale blue phosphorescent moss, high ceilings, shelves of manuscripts arranged in order. Approximately three hundred and forty volumes. Mira had managed them all alone. "Mira," Elara said. Then stopped. She didn't know what to say. She couldn't say "that must have been difficult" or "that's amazing." Both felt off the mark. Mira had already turned away. She stepped back from the door and looked deeper into the cavern, as if confirming the direction of the descent route. It was a gesture like locking away emotions themselves. "In areas with high collapse risk, you must follow my instructions at all times," Mira said. A calm, composed voice. As if the previous words had never been spoken. Elara closed her mouth. Kael had been watching the entire exchange from behind. He said nothing. Only his gaze lingered on Mira's back for a moment. —— The descent was quieter than expected. Mira led, Elara followed, and Kael brought up the rear. The pale blue light cast by the phosphorescent moss gradually dimmed. The deeper they descended, the fewer signs of luminescent creatures. "The temperature's dropping," Elara said. "Humidity increases at the deepest level. That's why the perceived temperature feels lower," Mira replied. Still facing forward, Mira answered. She tested each foothold on the stone carefully, choosing each step with deliberation. To Elara, it looked less like caution and more like pure tension facing an unfamiliar path. And then, they arrived. The first thing Elara sensed was the absence of sound. Throughout their descent, there had been the constant sound of water dripping. The sound of moisture traveling down rock faces, the faint sensation of fungi swaying in the distance. All of it was gone. A massive arch appeared ahead. Not just one. They continued in sequence. Stone pillars lined up, stretching deeper and deeper, and their form was not natural. Traces of precise construction. Even after twelve hundred years, they maintained their orderly contours. No phosphorescent moss grew on the surface. No signs of luminescent life. Not even the natural shimmer of bedrock—only darkness. "This is... the remains of the Spinthread Corridor," Elara whispered. Her voice had become small. Unintentionally. It felt wrong to speak loudly in this space. "The remains of a stable transit route that the Palimpsest civilization once constructed to connect all dimensions," Mira said. Mira's voice was also subdued. Not the explanatory tone from before the translation desk, but something more cautious, quieter. "It lost its function due to the Great Erasure—a historical revision incident where records, memories, and physical traces were simultaneously deleted from all dimensions. The Palimpsest civilization itself was erased from existence by this incident. From the memories of those who knew it, from documents that recorded it, from most of the structures it built—everything, all at once. This corridor is one of the rare exceptions," Mira said. Elara withdrew the prism from her coat pocket. An eight-sided crystal resting in her palm. The liquid light inside moved differently than usual. Rather than wavering, it was drawn toward the corridor's depths, tilting in that direction. "The light is moving," Elara said. "...Yes, it is," Mira replied. Mira's gaze turned toward the prism. Then, immediately, it shifted to the wall surface. She began observing the stone pillars, pulling out a magnifying glass to peer at the carved patterns. "I'll begin making rubbings. I'll press paper against the surface to copy the carved inscriptions. While I work, please examine the surroundings," Mira said. Kael was already moving. He proceeded along the wall, checking for possible entrances and exits. His footsteps were quiet. The same economical movements as on the deck of a ship. Not a wasted motion. Elara opened the manuscript records. Translation notes from the seventeenth volume that Mira had lent her before descent. She began cross-referencing the deepest level descriptions with the ruins before her eyes. The spacing of the pillars. The angles of the arches. The pattern of inscriptions on the walls— "Mira," Elara said. "...," Mira replied. "This manuscript says there should be thirty-six pillars in the column arrangement," Elara said. "That's correct," Mira replied. "But counting visually, I can only confirm twenty-nine, and the rest disappear into the darkness. When I cross-reference with the placement diagram in the records, there should be a central axis in the middle—" Elara said. "Elara," Mira said. Mira spoke without stopping her work. "Lower your voice," Mira said. "I'm sorry," Elara said. She returned to a whisper and continued with her notes. The prism still pointed toward the corridor's depths. The light had become thin, like a thread pointing to a single location. Eventually, Mira's hands stopped. Mid-rubbing. She remained motionless, paper still pressed against the wall. "What's wrong?" Elara asked. "...The inscriptions," Mira said. Mira's voice dropped even lower. "They contain a proper name recorded in the manuscript margins, with a corresponding heraldic symbol carved here," Mira said. She didn't finish. She offered no further explanation. She carefully peeled away the rubbing paper and opened the manuscript to cross-reference. Her profile looked slightly pale. It might have been the phosphorescent light, or it might not have been. "Too quiet," Kael said. His voice came from the corridor entrance direction. Kael had returned. His voice was subdued but clear. "Something's wrong with the atmosphere ahead," Kael said. Elara was looking at the manuscript pages. There was a specific passage in the seventeenth volume. When compared with the translation notes, its meaning— "Ah," Elara said. "Don't make a sound," Kael said sharply. Elara quickly covered her mouth and apologized in a whisper. "Sorry. I just understood what this passage means—" Elara said. "Not now," Kael said. "I agree," Mira said. Mira and Kael's voices overlapped at the same moment, an unusual occurrence. The two exchanged glances—expressions that seemed somewhat awkward, but tinged with tension. In that single moment afterward, the darkness ahead of the corridor began to move. —— Imagine the sound of glass shattering. Not one or two pieces, but dozens of layers overlapping, resonating from the walls, ceiling, and floor simultaneously. That sound echoing, amplifying, compressing the air itself—the voice of an echo-form was something like that. Elara had encountered echo-forms twice before. One at a time, scattered incidents. Even then, her legs had gone weak. This was different. "...There are many," Kael murmured. His voice was pure situational assessment, without smile or jest. His amber eyes rapidly scanned the darkness. Exit. Retreat. Possible routes. "The western route we came from?" Kael asked. "It will be sealed. With three or more positioned, the retreat is cut off," Mira said. Mira had already pushed the rubbings into her coat's interior. The papers from mid-rubbing too, and the manuscript. Her hands, which might or might not have been trembling, worked through the steps without skipping any. The echo-forms' outlines became visible. Distorted humanoid shapes. Like shards of glass clustered together, unstable forms. One, two, four—she stopped counting. There were more. Kael moved. He grabbed Elara's arm and pulled her away from the echo-forms' range. The motion was fast. No hesitation. Her balance broke. As Kael braced himself, the hem of his coat rode up. In the pale blue phosphorescent light, for just a moment, it was visible. A scar running across his chest. A burn mark. The pattern—not from an ordinary accident. Something hot had burned the skin broadly and deeply. Elara registered it.