The morning mist hung over Mizuho Village. The mountain air was crisp and cold. As Senkū retied his pack and exhaled a white breath, it dispersed and vanished almost immediately. The embers from last night's fire still held a faint warmth. He'd read the notebook there. The two of them standing side by side on the hill, listening to the children's laughter. It felt like a distant memory, even though it was only yesterday. "Ready?" Yomi stood before the village gate. Her deep purple long hair was loosely tied back, and she wore her usual white coat. The case notebook was tucked away in the bag at her shoulder—her hands were empty as she looked at Senkū. "[serious]We can leave right now" "Then let's go" Yomi started walking. Senkū fell into step beside her. "...I'm guessing this isn't about the road happening to be the same direction or anything like that, right? Not now" Yomi paused for a beat. "[cold]...Why are you even confirming that" "[serious]Not confirming. Recording" He pulled out his experimental notebook and said it casually. Before Yomi could furrow her brow, Senkū was already running his pen across the page. ——Yomi: "Hypothetically" deleted. Changed to assertive form. Observation date: This morning. Yomi glanced at the memo from the side. "[sarcastic]...What are you doing" "[serious]Observation record" "You're taking notes the moment I change a single word? What kind of nerve do you have" She was one step away from anger. But in the next moment, Yomi covered her mouth. Laughter had come first. "...Honestly" "[serious]What" "Nothing" Their footsteps echoed together through the mist. --- They entered the Kiso mountain path less than an hour's walk from the village. By the old maps, it was the route toward the Kiso Mountains. The path was narrow, with tree branches jutting out from both sides. The stones beneath their feet had been worn smooth by rain, polished to a slick shine. The sound of a ravine drifted from somewhere. Senkū and Yomi walked ahead, slightly apart from the others. The two of them had their experimental notebook and case notebook open, cross-referencing past data on Ishiyami patients from the Nouvi Grassland. Their conversation was brief and precise—not a single unnecessary word. Behind them, a little distance back—— "[whispers]Hey, are you listening? I've been here since the fourth episode——no, from the very beginning. Hierarchically speaking, I'm clearly above you, right" "[whispers]I'm the teacher's top apprentice when it comes to medicinal herbs. Our roles are different, so hierarchy doesn't matter" "It does matter! The right to walk next to big brother is first-come, first-served, obviously!" "If it's first-come, then I've been counting since yesterday——" "Yesterday is too short! I was doing experiments with him in the forest——" "Experiments? Didn't your right hand just turn to stone" Kazeru froze. "[sarcastic]...That's not relevant" "It's totally relevant!" Silver-white short hair and crimson short bob were glaring at each other in the middle of the path. Kazeru's golden eyes were sparkling, but his argument was losing. Kazeru suddenly turned forward. He tried to call out to Senkū and Yomi. "Hey, big brother! I need you to settle something for us——" The two turned around. But——Senkū and Yomi were walking side by side, completely absorbed in their notebooks. Senkū pointed at some numerical value, and Yomi gave a short nod. Yomi opened another page, and Senkū leaned in to look. Neither of them seemed unaware of Kazeru's voice, yet they showed no sign of turning toward him. Kazeru and Reina exchanged glances. "[whispers]...Isn't it kind of scary to interrupt them" "[whispers]Maybe they're research partners or something...I don't really understand it though" "[whispers]Yeah, it feels like we shouldn't step into that" Both of them took a step back simultaneously. They began walking in the rear, side by side. The hierarchy dispute had ended without anyone noticing. As they watched the two ahead, Kazeru and Reina naturally fell into formation beside each other. "[whispers]...Well, this is fine" "[whispers]Yeah. This works" The four of them' positions settled quietly, without anyone declaring it. --- That night, they camped on flat ground near the sound of a clear stream. Senkū built the fire. He arranged the firewood, struck the flint, and checked how it burned. He didn't say anything special about it, and neither did Yomi. But Yomi glanced at the sight for a moment, then after a brief pause, opened her collection bag. That first night, when she'd found Senkū by the river, Yomi had built the fire alone. Now Senkū was building it. A small change, quietly present. After dinner, Yomi called Kazeru and Reina over to the fire. "[serious]Medicinal herbs are completely different between mountains and flatlands. I want you both to learn what grows along the Kiso path before we enter the Nouvi Grassland" "[excited]For real! Is this a lesson!!" "You don't use much beyond wound treatment, but it's good to know anyway" "[excited]Got it!!" Reina began laying out several types of medicinal herbs from her collection bag. With a serious expression, she compared the shapes and colors of the leaves. Yomi stood beside her, explaining each one's name and effects. Senkū sat on the opposite side of the fire, watching them. Yomi's voice when she explained was slightly softer than usual. When Reina made a mistake, she corrected her quietly. When Reina answered correctly, she gave a short nod. When Kazeru asked an off-topic question, Yomi sighed but answered anyway. The firelight illuminated all three faces. Senkū suddenly spoke. "[serious]That thing you were trying to tell me before the petrification——is there another one" Yomi's hands stopped. Kazeru and Reina were focused on the herbs and didn't notice. Yomi looked at Senkū. "[cold]...How do you know that" "[serious]There seemed to be erased text before the opening of the last page. I could see the pencil marks" Silence fell. The sound of the river continued, constant. Yomi looked away from the herbs toward the flames. For a long time, she said nothing. Then, in a very small voice—— "[whispers]...Maybe. There's one more" That was all. Senkū didn't ask anything further. He didn't push. "[serious]I see" He replied briefly and kept watching the fire. Yomi turned back toward Reina and resumed explaining the herbs. Kazeru started to say, "Wait, weren't you two just talking about something important!?" but both of them were already ignoring him. --- The next morning, Yomi examined Kazeru's right hand. "Spread it out" Kazeru extended the tips of his right hand fingers. The petrified fingertips now had finer cracks running across their surface than yesterday. Yomi leaned in to check. "[serious]...The cracks are increasing. Since the petrification substance stopped flowing in more than half a day ago, natural recovery has begun" "[surprised]So it'll heal!?" "It'll be faster if we apply salve. We need a component that softens this area——Reina, do we have it among what we collected yesterday" Reina pulled out her collection bag and buried her face in it. She searched through it with a serious expression. Senkū spoke from the side. "[serious]If it works on petrification residue, it needs a component that interferes with calcium metabolism. Plus something that helps the epidermis retain moisture. Specifically——" Senkū listed several names. As Reina listened, she pulled out one herb, then another from the bag. She checked the leaf shapes, smelled them, and sorted them. There was little hesitation in her movements. "This one, and this one——oh, this too" "[surprised]...All correct" Yomi looked slightly surprised. Reina laughed with a small "ehehe." Yomi quickly processed the herbs into salve and gently applied it to Kazeru's fingertips. For a moment, no one spoke. Then, gradually——the color of the petrified fingertips began to change. The whitish parts slowly returned to normal skin tone. "[excited]Ah! It moved! My fingers moved!!" Kazeru waved his right hand through the air. "[cold]Stay still" "But they're moving! Look, look!!" "[cold]That's exactly why you shouldn't wave them around!!" Reina looked up at Senkū with joy in her eyes. "Teacher! I was useful!" "[serious]Not bad" Reina's face broke into a full smile. Then, as if remembering something, she glanced at Yomi. "[whispers]...Um, honestly, I'm happier getting approval from you than from the teacher" "[serious]Don't call me teacher. I'm not your teacher" "Then can I call you big brother!!" "[serious]I never gave you permission for that" "Huh, revoked!?" Reina laughed until she couldn't breathe. Yomi let out a small sigh, but the corners of her mouth had softened slightly. --- Past midday, the Kiso mountain path reached a high point. The trees opened up, and the view stretched far into the distance. A vast grassland spread beyond the mountains. A band of green and yellow stretching to the horizon——that was the Nouvi Grassland. They'd heard there were wild horse herds, but they weren't visible from this distance. Senkū's pocket vibrated. The portable wireless radio attached to his belt——a miniaturized version of the vacuum tube radio the Science Kingdom had revived, capable of receiving Morse code signals within a fifty-kilometer radius——began to emit a faint sound. Senkū stopped and checked the reception. As he decoded the message, his expression gradually changed. "[serious]...Message from the Science Kingdom. Emergency transmission" The three turned around. "[serious]A cluster of petrification aftereffects with different symptoms than Ishiyami has broken out in settlements around the Nouvi Grassland. Patient count has exceeded thirty. The Science Kingdom can't handle it alone, so they're requesting our support" No one spoke. Wind blew from the grassland direction. In the distance, the grass rustled. Senkū placed his hand on his chin. (Mizuho Village was water source contamination. A localized problem. But if we're seeing over thirty patients on a grassland scale——the petrification substance might be spreading through routes other than water.) "[serious]...Yomi. Check if detailed symptoms came through. I need data you can examine to see what's different from Ishiyami" Yomi nodded. "[serious]Patient skin symptoms and joint condition are most important, plus the infection timeline. Can you request additional transmission" "[serious]I'll request it" Kazeru looked toward the grassland. "[excited]There are horses in the grassland, right! That'd speed up our movement a lot!!" "[serious]That's correct judgment" "For real! I got praised right away! That's rare!!" "[serious]'Rare' is unnecessary" Reina gripped the strap of her collection bag tightly, staring at the grassland. "...Grassland medicinal herbs are completely different from mountain ones. I'm not sure if I can actually be useful——" Yomi stood beside her. "[serious]Do you remember what you could do in the last village" Reina looked up. "...Yeah" "Then just do the same thing" That was all. But Reina slowly composed herself and nodded. Senkū put away the wireless radio. "[serious]Let's go. The Nouvi Grassland" The four of them started walking. The path ahead descended from the high point toward the grassland. Why the petrification substance was spreading on a grassland scale. What routes existed besides water sources. No one knew the answers yet. But the four of them were going to find them. Without using words like "hypothetically."