After changing into brand-new, thick clothes made from fire felt grass, she finally felt secure and comfortable.
Once they were both ready, their gazes returned to the makeshift wooden hut in the forest.
It was the simple shelter Senku had barely managed to build after waking up.
With its log frame and roughly fitted planks, it looked crude from every angle. Gaps riddled the walls, and the whole structure seemed ready to collapse. It could barely keep out the wind and rain, let alone offer any real stability.
Li Xiang slowly circled beneath the trees around the hut, reaching out to give one of the supporting wooden posts a gentle push.
At the slightest pressure from her fingertips, the entire post wobbled. A faint creak came from the joints between the planks, a sound that inspired little confidence.
She withdrew her hand and turned toward Senku beside her. "This hut doesn't look very sturdy. A strong wind would probably make it sway. Should we reinforce it?"
At her words, Senku picked at his ear and looked over the little wooden hut he had built.
His gaze swept across the loose planks and drafty gaps. He nodded slightly, as though it were only natural.
"Well, you've got a point."
It really was too crude.
Sturdy reinforced-concrete buildings were everywhere in modern civilization. Now that they were suddenly living in a primitive wooden shack, it hardly took any thought to realize how inadequate it was. It could withstand neither storms nor wild animals, and there was no way it could serve as a long-term base for the Kingdom of Science.
Senku settled on a plan immediately, his tone light. "Easy. We just coat the outer walls with concrete. That'll reinforce the whole thing, make it durable and waterproof."
Li Xiang frowned at once, confusion in her eyes.
"Concrete? We're in the middle of nowhere, deep in the mountains, with no settlement anywhere nearby. Where are we supposed to find sand? How can we make concrete without it?"
That was the most obvious problem.
Sand was an essential ingredient for cement concrete, but apart from vegetation and rocks, there was no sign of fine sand anywhere in this forest.
Rather than looking troubled by her question, Senku curled his lips into a supremely confident smile.
"No need to worry. We don't have to go looking for sand. We can make the most primitive kind of cement with materials right here."
As he spoke, Senku crouched down, rummaged briefly through the scattered stones on the ground, and picked up a few grayish-white rocks.
The rocks were hard, with a faintly matte surface. They looked like utterly ordinary stones from the mountains.
"Look at this. Limestone."
He held a rock up before Li Xiang's eyes and explained patiently and carefully.
"This is the key ingredient for making cement. First, we build a fire and roast this limestone at high temperatures for a long time. Once it's been heated long enough and burned all the way through, the hard limestone will break down and crumble, giving us quicklime."
"Quicklime reacts violently with water. Add enough water to slake it completely, then leave it to mature for a while, and it becomes slaked lime."
Li Xiang listened quietly, carefully committing each step to memory.
"Slaked lime alone isn't hard enough. It won't do much to reinforce the house, and it won't reach the strength of concrete."
Senku pointed toward the faint outline of Mount Fuji in the distance and continued.
"But we have a natural advantage here. We're right next to Mount Fuji, and volcanic ash is scattered all over the forest floor."
"Mix slaked lime with natural volcanic ash in the right proportions, add water, and stir thoroughly. That gives us the classic hydraulic volcanic-ash cement used in ancient times."
At that, Li Xiang instinctively asked, "Volcanic-ash cement?"
"Exactly."
Senku nodded, gesturing briefly in the air to illustrate the proportions as he continued his orderly explanation.
"Lime and volcanic ash alone still aren't ideal. We'll mix in a little fine clay to improve adhesion. Later, when we have time to find some fine sand and gravel by a river, we can add that too. It'll double the overall strength, giving us a basic version of concrete."
"Spread the cement slurry evenly over the hut's outer walls and let it dry and harden naturally. The whole hut will be wrapped in a hard cement shell, making it sturdy and waterproof."
Then Senku briskly summed up the entire process.
"The whole process is simple. First, gather enough limestone and burn it over a strong fire for a long time to make quicklime. Add water to slake it, then leave it to mature. Meanwhile, collect plenty of volcanic ash and sift it carefully, removing stones, weeds, and other impurities. Finally, mix the slaked lime, volcanic ash, and a little clay in the right proportions, add water, and stir well. Spread it over the outer walls while it's still hot, then just wait for it to harden."
He looked up at the crude wooden hut before him.
"Once the cement coating is completely dry and set, this house will be perfectly safe. We won't have to worry about wind, rain, or wild animals anymore. This will be the first secure base of our Kingdom of Science."
After hearing him out, Li Xiang smiled.
"The great scientist Senku."
"I have to admit, that really is an excellent idea. An ordinary person in this primitive world, with absolutely nothing to work with, would never think of making building materials this way to reinforce a house."
Then she changed tack, looking at the enthusiastic Senku as she spread her hands slightly.
"But you seem to have forgotten the most important thing."
Senku raised an eyebrow at her.
"The two of us simply don't have enough manpower."
Li Xiang looked at him.
"I'm definitely a lot stronger than you, both physically and in a fight. I handle pretty much all the heavy work, but there are just too many materials, and they're too heavy."
"Limestone, volcanic ash, clay-we need to gather and haul large quantities of every single one. It's all hard manual labor."
She estimated the workload and said frankly, "If it's just the two of us chipping away at it, that's a huge project. Conservatively speaking, it'll take at least a full month just to finish reinforcing this little hut."
At her words, Senku's enthusiasm faltered slightly.
He rubbed his chin and thought seriously for a couple of seconds, then had to admit that Li Xiang was right.
No matter how perfect the scientific method was, someone still had to put it into practice.
With only two people tackling such a complicated, physically demanding project, their efficiency would be painfully low. It would take far too long.
After a brief silence, Senku slowly nodded. "That's true."
Seeing the boy look a little deflated, Li Xiang chuckled. Her tone relaxed, without a trace of impatience.
She stepped forward, patted Senku on the shoulder, and gently reassured him.
"But that's all right."
"We can take it slowly. In a world where we're starting from scratch, the worst thing is having no direction. Now that we've found a way, all we have to do is keep working steadily. That makes things much simpler, doesn't it?"
As Senku watched Li Xiang gently reassure him, a sudden gleam flashed in his eyes.
As though he had abruptly remembered something important, his eyes lit up, and he immediately raised a hand to stop her.
"Li Xiang!"
Li Xiang broke off and turned toward him in confusion. "What is it?"
Meeting her puzzled gaze, Senku straightened. His eyes brimmed with certainty and excitement, and fresh enthusiasm instantly flared through him.
"Let's put reinforcing the house aside for now. There's something else we should do first."
His tone was utterly serious. "I'm ten billion percent certain you'll be interested in this."
Now thoroughly intrigued, Li Xiang raised her eyebrows slightly and asked, "Oh? What is it?"
Senku smiled. "You'll find out when we get there. Come with me somewhere, and you'll understand."
"I don't know what little Senku is planning, but I trust you." Li Xiang followed Senku's lead, slowly moving to his side, and the two left the base at an easy, unhurried pace.
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