"What is that rascal up to these days..."
Sejong muttered as he gazed out the window, taking a brief respite from his duties with the ministers.
The 'rascal' he referred to was Hyang.
After taking a considerable amount of resources and manpower, Hyang had not been seen in the main hall for quite some time.
"Can I skip the afternoon performance?"
"Is it something you must miss?"
"Yes."
"Then do as you wish."
With Hyang's firm response, Sejong reluctantly granted permission.
As soon as Sejong's approval was given, Hyang began to bustle about with the people he had gathered.
The problem was that, while they were busy, they did not disclose what they were doing.
No, they did provide some information.
"We are conducting research for the livelihood of the people of Joseon and the national defense. However, there is a problem."
"A problem?"
"It takes a bit of time to understand the knowledge of arithmetic and to compile the experience into written documents."
"Is that so? Hmm..."
Sejong nodded after staring at Hyang in silence for a long while.
"I trust you, my son."
"Your Majesty's trust will not be disappointed."
A few days after the Mid-Autumn Festival, Hyang and Jeongcho made a presentation in front of Sejong and the ministers.
"This is the research conducted by myself and the officials of the research institute."
"Yes, what is it?"
"We have formulas to adjust the calendar from Ming to fit our Joseon."
"Oh?" Sejong and the ministers showed interest in Hyang's announcement.
Receiving the attention of Sejong and the ministers, Hyang continued with the presentation.
"You may remember the old-style ceremony that took place a few years ago. At that time, due to a mistake by the Seowon, the timing was off, and the person in charge, Lee Cheonbong, was punished. Your Majesty may recall this as well."
Sejong nodded at Hyang's mention.
"I remember."
The incident in question occurred in the fourth year of Sejong's reign.
On January 1st of that year, a solar eclipse was predicted.
According to tradition, Sejong and the ministers wore mourning clothes and prepared for the old-style ceremony.
However, the eclipse began one watch later than the time predicted by the Seowon.
As a result, Lee Cheonbong, who was in charge of the eclipse forecast, was punished.
Using this past event as an example, Hyang continued his explanation.
"The reason such a disastrous event occurred was that the calendar from China did not align with our Joseon. To correct this, we researched arithmetic formulas to adjust the calendar."
Hyang paused and gestured to the attendants behind him.
The attendants, seeing Hyang's gesture, handed out thick books to Sejong and the ministers.
"Arithmetic for Calendar Adjustment, Volume 1? Quite straightforward."
"We are also considering a name change if necessary."
Sejong opened the book after reading the title and examined its contents.
The formulas written to adjust the solar terms used in Ming to fit the realities of Joseon were recorded in a complex manner.
"This is good. It will be helpful in many ways."
"As you can see from the title, it is not yet a completed version."
At Hyang's words, Sejong looked again at the title and contents before gazing at Hyang.
"Of course, the title suggests that. But looking at the content, it seems quite usable already."
Sejong, who had some understanding of arithmetic, highly valued the formulas written in the book.
However, Hyang shook his head.
"There are still many errors. What is written in the book is only a rough outline. It needs to be corrected. Otherwise, errors will occur every year."
"But?"
At Hyang's response, Sejong's expression turned to one of disappointment as he clicked his tongue.
"Then I will wait for the proper version. Work hard."
"Yes, Your Majesty."
With that response, Hyang once again locked himself away in the research institute with his people.
After that, as the end of the year approached, there was still no news.
No, it wasn't complete silence.
Among the scholars, those skilled in arithmetic were recruited as instructors, and the number of people increased.
They brought in the astronomical calculation book from Ming through regular trade and sent people throughout Joseon to measure the stars, moving busily.
And every time such activities took place, Hyang diligently prepared reports to submit to Sejong.
"A celestial observation instrument? What is that?"
"It is a device for observing celestial bodies, as the name suggests."
"The report is a bit lacking, isn't it?"
At Sejong's remark, Hyang glanced at the historians and ministers and replied in a small voice.
"I will submit a separate report later. Externally, this level is appropriate."
"Hmm?"
Sejong sighed as he pondered the implications of Hyang's response.
"Hoo~. I understand what you mean."
That night, Sejong climbed to the pavilion alone and sighed as he looked toward the East Palace.
"Hoo~. It seems that both I and the nation are weak, and you are bearing a heavy burden."
The celestial observation instruments Hyang mentioned were the Ho Cheon Gi and the Dae Gan Gi, as well as the So Gan Gi.
To create these devices, Jang Yeong-sil and the craftsmen worked tirelessly through the night.
Until the results were produced, the officials of the research institute traveled across the country with the observation instruments brought in from Ming, either officially or through smuggling.
However, the reason Hyang did not report all of this in detail was due to diplomatic relations with Ming.
Observing the heavens could become a significant diplomatic issue considering the tributary relationship with Ming.
For that reason, the calendar reform was expressed as "correcting the calendar given by Ming" rather than "using an independent calendar," and the celestial observation instruments were simply reported as ordinary observation devices.
In this way, Hyang devised a plan to prevent any direct harm to Sejong, regardless of what Ming might later say.
Knowing why Hyang acted this way, Sejong sighed.
For that reason, he had been suppressing his curiosity, but what Sejong was truly curious about was the military field.
After submitting a report on developing a new cannon with Lee Cheon and Choi Hae-san, Hyang did not submit any further reports.
"Why hasn't the Crown Prince submitted any reports?"
"It is a matter being conducted in utmost secrecy, so please give me a little more time."
"You know well that without a report, it is difficult to execute the budget, right?"
"Just a little more time, please. And since we're on the subject, could we increase the budget a bit more..."
"You rascal!"
Even though Sejong was furious, Hyang remained tight-lipped.
It wasn't just Hyang; Choi Hae-san and Lee Cheon were the same.
No matter how much Sejong and the ministers coaxed and pleaded, the two men kept their mouths firmly shut.
"Must I endure until that rascal decides to reveal it?"
Sejong forced himself to suppress his curiosity, but the activities Hyang was undertaking were growing larger by the day.
Due to a major incident in Ming and the Jurchens, Sejong accelerated the pace of the military reforms he had been planning.
As part of this reform, the existing training hall was expanded into a training institute, and Hyang requested support from Sejong.
"You want support for the military officers and soldiers of the training institute? Why?"
"We need those who can actually handle the newly created weapons."
"Hmm..."
Sejong, squinting at Hyang, showed a helpless expression.
"Sigh! It can't be helped. I will grant it."
"And could we increase the budget a bit more..."
"You rascal! Get out!"
Thus, a significant number of military officers and soldiers from the training institute were assigned to Hyang.
With the personnel support, Hyang built a training ground for them, located in the southeast near the foot of Namsan.
Interestingly, the military officers and soldiers assigned in this manner also kept their mouths tightly shut.
While there were those among the conscripted military officers and soldiers who liked to gossip, for some reason, they all kept silent regarding what Hyang was doing.
Moreover, the area where the conscripted military officers and soldiers trained was surrounded by high, dense wooden fences, and the soldiers stood guard with strict vigilance.
Within that concealed area, loud explosions could be heard every day.
As a result, Sejong, the ministers, and all the residents of Hanyang were focused on this forbidden place—the entrance to the training ground, marked with a sign reading "Area 51."
As time passed, rumors began to leak out, roughly stating, "A tremendous cannon has been developed," and "Not just one against a hundred, but a weapon unique to one."
Along with these rumors, a new phrase began to circulate: "Game Changer."
"Game Changer? What does that mean?"
"It is what they say."
At the response from the attendant who reported the rumors, Sejong nodded unconsciously.
"It must be from the Crown Prince."
Guessing the source, Sejong glanced at the clock.
After checking the time, he clicked his tongue.
"It is time to be at the military training center."
While Hyang was causing headaches for the Ministry of Finance with various activities, it was not easy for Sejong or the ministers to say anything to him.
Both Sejong and the ministers were overwhelmed with heavy workloads, but Hyang's work intensity was no less.
Regardless of summer or winter, he rose at myoshi (6 a.m. sharp), attended the morning court, and practiced martial arts in the afternoon.
During other times, he moved between the research institute, the military training center, and Area 51 to carry out his duties.
To reduce travel time, Hyang began to ride horses, and the sight of Hyang and his escort moving busily on horseback became a new spectacle in Hanyang.
After a busy day, Hyang would go to bed around the time of haesimal (just before midnight).
Before establishing the research institute, he had gone to bed later than that, so Sejong and Queen Sohyeon were rather pleased.
"I was worried you weren't sleeping enough, but I'm relieved!"
"Indeed."
Whether he knew of the situation or not, Hyang measured his height against the doorpost every night before going to bed.
Watching his height grow day by day, he felt satisfied.
"This is the peak of my growth period; I must sleep well! By the way... horseback riding is quite beneficial in many ways?"
Hyang's healthy routine was welcomed by the ministers, as the troublesome figure who always caused headaches had disappeared.
Of course, in cases of significant events, such as the important incident in the latter half of the Gapjin year, Hyang had still visited the court regularly, but that was a welcome occurrence.
However, as the end of the year approached, the ministers found it increasingly difficult to suppress their curiosity.
Immediately after the Mid-Autumn Festival, the inner court guards were included among those who had become curious.
Sejong seemed to have some knowledge about the inner court guards, but he too kept his mouth shut.
"Your Majesty! I believe we need to verify the results of the Crown Prince's recent activities."
"Indeed! The funds entering the Crown Prince's research institute are not insignificant. We must check whether the budget is being used properly."
Ultimately, as December arrived, the ministers, unable to contain their curiosity, rose up in unison.
Seeing the united front of the ministers, Sejong nodded.
"I agree. Bring the Crown Prince here."
"Yes, Your Majesty."
A short while later, a horse carrying the royal messenger galloped out of Gwanghwamun.
After about half an hour, Hyang entered the court, catching his breath.
After bowing to Sejong and taking his seat, Sejong spoke.
"I have been aware that you have been undertaking many tasks since last spring. Among them, I know that there are good results, such as the correction of the calendar, even if it is incomplete. It is truly commendable to see such results at your young age."
"Thank you very much."
Hyang bowed his head at Sejong's praise.
"However, that is where the praise ends. There have been many other matters, but neither I nor the ministers have received proper reports. This is different from the promise you made to me and the ministers at the beginning. What did you write in the plan you submitted when you first established the research institute? You promised to thoroughly disclose the expenses used in the institute, did you not?"
"I apologize. However, it was a matter that required utmost secrecy..."
"Is there a confidentiality that even I and the ministers must adhere to?"
"It was related to the national defense of our Joseon, so it needed to be kept as confidential as possible until the final product was completed. Just in case."
"Hmm..."
Sejong fell into thought for a moment at Hyang's response.
Looking at the prostrated Hyang, Sejong spoke.
"We cannot continue to execute the budget based solely on your words under the pretext of confidentiality. Even if it is a mid-process, we must conduct a review. We must avoid wasting precious resources on futile matters. Therefore, I will conduct an audit of your activities. How long will it take to prepare?"
After calculating for a moment, Hyang replied.
"Please give me five days."
"Very well. I will execute the formal audit in five days."