“A Western design, I see. It will be expensive, as it requires special craftsmen, but it should be manageable. Or, I could just make it myself.”

Himself? Glass windows?

I looked at Yoo Ho with questioning eyes. The blueprint I had drawn included a very large, single pane of glass for one of the walls. A rectangular glass wall would dramatically increase the amount of natural light.

This guy is really suspicious. No, forget it. What’s important is the Vitamin D, right?

What I had designed was a triple-paned glass window. I had completely removed the function of opening and closing it. It was less a window and more a wall made of glass. For convenience, of course, a curtain was also part of the design. I had drawn a separate, smaller window for ventilation, also made of glass. The whole thing looked like it had been designed by someone who had at least dabbled in architecture.

Could Yoo Ho really make all of this?

Yoo Ho stroked his chin with his fingers, then spoke. “If this had been nonsense, I was planning on giving you a piece of my mind, but this is beyond anything I could have imagined. And I am certain it will be effective. It is worth attempting, whether it succeeds or not.” He frankly admitted his misjudgment. It meant that his trust in me was beginning to grow. I felt a little pleased.

“It goes without saying… but the faster, the better, right?”

“Considering the Master’s condition, of course.”

“Excellent. I will have the stove and the windows installed within the day. For the ondol, I will have to summon a master craftsman and start from the construction phase.” He rubbed his chin, lost in thought, before adding, “It will require additional work to move the Master’s quarters to another location, but… it should not take more than ten days.”

Yes! With this, I can significantly alleviate the Master’s symptoms.

Ondol. For any veteran reader¹ of so-called “fusion” martial arts novels, it was one of those things you look up on the internet at least once. There’s a reason protagonists who get transported to another world always start by building an ondol.

Phew, I’m so glad I watched that documentary to the very end!

I could manage the design, but the actual construction required an expert. Suddenly, I realized something strange in what Yoo Ho had said.

“Wait a minute, you’re going to make the stove and windows in a single day?”

“Yes, is there a problem?” Yoo Ho looked at me as if I were asking the obvious.

Come to think of it, this guy knows some kind of martial arts. If he says it’s possible, I guess it’s possible. But how?

In the end, I couldn’t contain my curiosity. “How?”

“Hahaha, did you think you were the only one with secrets, Young Master?”

“Ugh.”

He’d hit the nail on the head.

“My secret may be nothing compared to yours, of course,” Yoo Ho said. “But still. You did get the better of me this time…”

“So you’ll tell me?”

“No. I’m a petty man. I have to at least make you this curious.” He grinned playfully.

I had initially thought he was a scary bastard whose thoughts were impossible to read, but now I saw he had this side to him, too.

“If it turns out well, I will have them installed in your room as well, Young Master. This is your achievement, after all,” Yoo Ho said. His tone was nonchalant, but his voice was laced with a deep sense of gratitude.

***

One day later. When I woke at dawn and went outside, Yoo Ho was already removing the existing wooden window frames and installing the new glass ones.

He actually made it. How did he make it so fast? It hasn’t even been ten hours. It’s not like he has modern tools or equipment.

A thick cloud of doubt filled my mind, but I decided to let it go for now. The important thing was that the glass windows were installed! Right next to the room, a new structure was already being built. Seeing them laying the ondol flues first, I was amazed by their incredible speed.

He summoned master craftsmen and put them to work in a single day. This is insanely fast.

Though slightly different in form from what existed on Earth, glass was still glass. Moreover, it was a triple-paned window, providing a much better seal than the old wooden one.

“Now that it’s installed, the house looks much brighter, doesn’t it, Young Master?”

“Yes. A lot of sunlight will come in.”

Before, you had to open the window to get sunlight. Now, there was no need.

To be honest, I thought the glass window would be harder to make than the ondol, but he managed it this quickly. And it wasn’t as if glass was common in this world. Even the Cloud-Dragon Escort Agency used wooden windows with pasted paper.⁵ In human history, the popularization of glass windows came much later. Well, this world is different from the real Earth in many ways.

I scratched my head.

“Ah, the stove installation is also finished,” Yoo Ho said. “The Master is inside.”

“Really?”

I hurried inside. A cozy warmth filled the room. My master, Zhuge Rin, was sitting in a long chair, leisurely reading a book. Warm sunlight poured in from the large glass window, bathing him in its glow. He looked so dazzling, it was like a scene from a movie.

To be able to close the window in winter and still have the stove on… it’s so warm. And with the improved lighting from the glass, this must have bought him a lot of time.

I felt a surge of happiness as I looked at the completely transformed room. The sight of Zhuge Rin sunbathing while reading was so peaceful.

“Ah, Hee-ya, you’re here.”

Sensing my presence, Zhuge Rin looked up. My face flushed as he called me by the nickname. At my age, it was hard to get used to being called such a name.

Is this what it would have felt like to have parents?

“Come in,” White Qilin, Zhuge Rin, said to me. “I cannot tell you how wonderful it is to be able to close the window while using the stove. My body has truly warmed up. I feel as if I am soaking in a hot spring.”

“How are you feeling?”

“Until yesterday, I was coughing all day and my throat was sore, but it has subsided a great deal. To think a stove could be this wonderful… Hee-ya, now that I’ve used it, I understand what an incredible thing you have made.”

Zhuge Rin patted the seat next to him, urging me to sit.

The chair seems so big because I’m small.

My little body scrambled up onto the chair. Zhuge Rin beamed, as if finding my struggle adorable.

“My dear Hee, how can you be so clever and so cute? No one has ever thought to install a glass window to let in the sunlight while raising the indoor temperature. The matriarch of the Namgoong Clan is always boasting about how amazing her successors are, but I doubt they could hold a candle to you.”

“Ehehe!”

“And what about this stove? It’s incomparably warmer than a fireplace or a brazier. I wonder why I only learned of such a thing now.”

No, Master, it’s because glass is incredibly expensive in this era, and they don’t have the technology to make such large panes.

I still had no idea how that extra, Yoo Ho, had managed to whip up a glass window in a single day.

And when did he make the stove while he was making the window? Is he using alchemy or something?

I was beginning to suspect Yoo Ho’s true identity. Realistically, producing such a glass window in one day was absolutely no ordinary feat.

Yoo Ho… I’ll have to look into him later. His loyalty to the Master is extraordinary, but there’s something suspicious about him. Still, the Master is so happy. That makes me happy, too.

It hadn’t been long since I met Zhuge Rin, but he was a man whose love for his disciple was far deeper than I could have imagined. Just look at him now. His doting praise³ was enough to give me goosebumps.

“All this time, I knew nothing but the medical arts,” he said. “I was a frog in a well. You have removed the scales from my eyes.”

Unable to endure his doting any longer, I finally cried out, “Aah, Master, please!”

“What is it?” My master tilted his head, then spoke to a servant who was waiting nearby. “Ah, bring some sweets. Our Hee must be feeling peckish. He is still a child, he must eat a lot.”

At his master’s urging, the servant scurried to the kitchen.

***

Yoo Ho did not follow me inside, but he hadn’t left either. He stood just outside the door, listening intently to the voices within. He let out a sigh.

When he first saw Jin Cheon-hee, he took a liking to him, and now he’s become a complete doting fool.

Who was the Divine Physician? He was the peerless physician and the last heir of the Zhuge Clan. Aside from the professional smile he used when necessary, he rarely smiled in his personal life. And as his health worsened day by day, the pavilion had been filled with nothing but silence and pained groans. But since meeting Jin Cheon-hee, the laughter never seemed to cease.

So this is why people raise children.

And he wasn’t just any child; he was a child full of secrets. From the moment he arrived, the boy had begun to change the chilly atmosphere of the medical pavilion. For Yoo Ho, that was a small but significant change.

And there were tangible changes as well. The color had returned to Zhuge Rin’s face. For his master, who was rapidly losing his body heat due to the Nine Yin Severed Meridians, the warmth of that sealed room was a precious thing, essential for extending his life. The glass window, and the bronze stove that vented its smoke outside—these two things alone would sustain Zhuge Rin’s health for a considerable time. And when the ondol system, currently under construction, was added to that, how much better would it be?

This was incredibly valuable to Yoo Ho.

So he wasn’t just talking empty words. But his knowledge is still suspicious. The Master may not care, saying his life is short anyway, but…

Lost in thought, Yoo Ho’s expression turned fierce.

Jin Cheon-hee. If you truly save my master’s life, I will give you anything. Even this life of mine.

A venomous energy that no one could have detected flowed from between his narrowed eyes. Then, just as suddenly, his expression softened. From inside, he could hear Zhuge Rin’s laughter. The venom in Yoo Ho’s eyes vanished without a trace.

How many years has it been since the Master laughed like that…?

A smile touched Yoo Ho’s lips.