Sejong, who had been taking a brief rest after reviewing state affairs with his ministers, muttered to himself as he looked out the window. The 'guy' Sejong was referring to was Hyang.
* * *
After securing people, buildings, and a considerable budget, Hyang rarely appeared in the main hall.
"Can I skip the afternoon performance?"
"Is there something you absolutely have to do?"
"Yes."
"…Do as you wish."
Sejong, after some deliberation, allowed Hyang's firm answer.
As soon as Sejong's permission was given, Hyang began to move busily with the people he had gathered.
The problem was that he did not reveal what he was doing, even as he moved busily. Or rather, he did reveal it.
"We are conducting research for the benefit of the lives of Joseon's people and the defense of the nation. However, there is a problem."
"Problem?"
"I have some knowledge of arithmetic, but it takes time to turn experience into written documents."
"Is that so? Hmm…"
Sejong, who had been silently looking at Hyang for a while, nodded.
"Your father, the Crown Prince, trusts you."
"Your Majesty's trust will never be disappointed."
A few days after the Mid-Autumn Festival, Hyang and Jeong Choe made a presentation to Sejong and the ministers.
"This is the result of the research conducted by myself and the officials at the research institute."
"Really? What is it?"
"These are the formulas for adjusting the calendar from Ming to fit our Joseon."
"Hmm?"
Sejong and the ministers showed interest in Hyang's presentation. Under their watchful eyes, Hyang continued.
"You may remember the Guseokrye (救餘禮) that happened a few years ago. Due to a mistake by the Seoungeon, the timing was off, and the person in charge, Lee Cheonbong, was punished. Your Majesty may also remember this."
Sejong nodded at Hyang's reminder.
"I remember."
The incident in question occurred in the fourth year of Sejong's reign.
On January 1, 1422, a solar eclipse was predicted. Following the precedent, Sejong and the ministers put on mourning clothes and prepared for the Guseokrye. However, the solar eclipse began one hour later than the time predicted by the Seoungeon. As a result, Lee Cheonbong, who was responsible for the solar eclipse prediction, was punished.
Using this past incident as an example, Hyang continued his explanation.
"The reason such a grave mistake occurred was that the Chinese calendar did not fit our Joseon. To correct this, we have been researching mathematical formulas to adjust the calendar."
Hyang, who paused in his speech, gestured to the eunuchs standing behind him. The eunuchs, seeing Hyang's gesture, distributed thick books to Sejong and the ministers.
"Calendar Adjustment Mathematics (層法修整算學 1次)? Very straightforward."
"If necessary, I am considering renaming it."
Sejong, having read the title, opened the book and examined the contents. The formulas for adjusting the calendar used in Ming to fit the conditions of Joseon were intricately recorded.
"Good. This will be very helpful in many ways."
"As you can see from the title, it is not yet a completed version."
Sejong, hearing Hyang's words, looked at the title and contents again before looking at Hyang.
"Of course, the title suggests that. But from the content, it seems already quite usable?"
Sejong, who had a certain expertise in arithmetic, highly evaluated the formulas written in the book. However, Hyang shook his head.
"There are still many errors. The content written in the book now is just a rough estimate. It needs to be corrected. Otherwise, errors will occur every year."
"But…?"
Sejong, filled with regret, clicked his tongue at Hyang's answer.
"Then, I will wait for the proper version. Work hard."
"Yes, Your Majesty."
With that, Hyang returned to the research institute with the people and immersed himself in work again.
After that, even as the end of the year approached, there was no news. Or rather, it wasn't completely silent.
The number of people increased as he hired those skilled in arithmetic from among the Huihui (回回) people, and he brought in the Da Tong Tong Gui (大統通軌), a calendar calculation book from Ming, through regular trade routes. He also sent people across Joseon to measure the stars, moving busily.
And every time he did these things, Hyang submitted a report to Sejong.
"Observational instruments? What are these?"
"Exactly as it sounds, instruments for observing celestial bodies."
"The report is a bit thin, isn't it?"
Sejong's criticism made Hyang look around at the historians and ministers before answering in a low voice.
"I will submit a more detailed report later. For now, this level is appropriate for external reporting."
"Hmm?"
Sejong, pondering the meaning of Hyang's answer, sighed.
"Phew~. I understand what you mean."
That night, Sejong, alone on a pavilion, sighed as he looked in the direction of the Donggung.
"Phew~. Because this father and the country are weak, you have to bear such a heavy burden."
The observational instruments Hyang mentioned were the Zetianyi (澤天儀) and the Dajianyi (大簡儀), and the Xiaojianyi (小簡仪). To make these instruments, Jang Youngsil and the craftsmen worked tirelessly, day and night.
Before the results were out, the officials at the research institute and the soldiers used the observation instruments brought in from Ming, either officially or through smuggling, to travel around the country.
However, the reason Hyang did not report everything in detail was due to diplomatic relations with Ming. Observing the heavens could become a significant diplomatic issue considering the tributary relationship with Ming. Therefore, the calendar was expressed as 'correcting the calendar given by Ming' rather than 'using an independent calendar,' and the observational instruments were reported as simple celestial observation tools. This was Hyang's strategy to ensure that even if Ming raised objections later, Sejong would not suffer direct harm.
Sejong sighed because he understood why Hyang did this.
* * *
While suppressing his curiosity, Sejong was truly curious about the military field.
After reporting that he was developing a new cannon with Yi Cheon and Choe Hae-san, Hyang stopped submitting reports.
"Why isn't the Crown Prince submitting reports?"
"Since it is being conducted in extreme secrecy, please give him a little more time."
"Without a report, it is difficult to allocate the budget, don't you know?"
"Please give me a little more time. And while we're at it, a little more budget…"
"You brat!"
Despite Sejong's anger, Hyang remained silent. Not only Hyang, but Choe Hae-san and Yi Cheon also did the same.
No matter how much Sejong and the ministers tried to coax them, the two men's sealed lips never opened.
"Do I have to wait until that brat reveals it?"
Sejong forced himself to suppress his curiosity, but the scale of Hyang's activities was growing.
Due to the large-scale incidents in Ming and the Jurchen, Sejong accelerated the military reforms he had been planning.
As part of these reforms, the existing Hyeonryun-gwan (訓鍊觀) was expanded into the Hyeonryun-won (訓鍊院), and Hyang requested support from Sejong.
"Support the military officials and soldiers of the Hyeonryun-won? Why?"
"We need people who can actually handle the new weapons we are developing."
"Hmm…."
Sejong, who had been squinting at Hyang, made a face of resignation.
"Fine! I have no choice. I will allow it."
"And a little more budget…."
"You brat! Get out!"
As a result, a significant number of military officials and soldiers from the Hyeonryun-won were assigned to Hyang. With this support, Hyang built a training ground for them, located on the southern slope of Namsan, south of the military equipment office.
Interestingly, even the military officials and soldiers assigned to this task had their mouths tightly sealed.
Among those assigned, there were some who liked to gossip, but for some reason, they all kept silent about what Hyang was doing.
Moreover, the area where these assigned military officials and soldiers trained was surrounded by tall and dense wooden fences, and soldiers stood guard strictly. Inside, loud explosions could be heard daily.
As a result, not only Sejong and the ministers but also all the residents of Hanyang were focused on this forbidden place—the sign on the gatepost blocking the entrance to the training ground read 'Area 51.'
As time passed, rumors began to leak out, roughly stating that 'an amazing cannon has been developed' or 'a weapon that can handle a thousand enemies is being made.' Along with these rumors, a new term became popular: 'Game Changer.'
"Game Changer? What does that mean?"
"It's what the scholars are saying."
Sejong, hearing the eunuch's report, nodded involuntarily.
"The Crown Prince, indeed."
Guessing the source, Sejong looked at the clock. Checking the time, Sejong clicked his tongue.
"It's time he should be at the military equipment office."
* * *
While causing headaches for the Ministry of Personnel with various activities, it was not easy for Sejong or the ministers to criticize Hyang. Both Sejong and the ministers were overworked, but Hyang's workload was no less.
Regardless of summer or winter, he woke up at 6 a.m. sharp, always attended the morning performance, and received martial arts training in the afternoon. In his spare time, he shuttled between the research institute, the military equipment office, and Area 51. To reduce travel time, Hyang started riding a horse, and the sight of Hyang and his guards moving busily on horseback became a new attraction in Hanyang.
Hyang, who ended his busy day and went to bed around midnight, was actually appreciated by Sejong and Queen Soheon because he used to sleep even later before the research institute was established.
"I was worried about your lack of sleep, but it's fortunate!"
"Yes, Your Majesty."
Whether he knew it or not, Hyang measured his height against the door frame every night before going to bed. Seeing his height grow day by day, Hyang was satisfied.
"You're in your growth spurt, so you must sleep well! By the way… riding a horse is helping in many ways?"
The ministers also welcomed Hyang's disciplined daily routine because the person who used to cause them headaches, like a troublesome sister-in-law, was no longer around.
Of course, when important events occurred in the latter half of the Gapsin Year, Hyang would visit the palace regularly, but this was a welcome change. However, as the end of the year approached, the ministers also found it hard to suppress their curiosity.
This was because, immediately after the Mid-Autumn Festival, the Neogunwei (內禁衛) was included among those who had become tight-lipped.
Sejong seemed to know something about the Neogunwei, but he, too, kept his mouth shut.
"Your Majesty! We need to review the results of the Crown Prince's recent activities."
"Indeed! A considerable amount of funds is being allocated to the Crown Prince's research institute. We need to verify if the budget is being used properly."
Finally, in December, the ministers, unable to contain their curiosity, rose up.
Sejong, seeing the united front of the ministers, nodded.
"I agree. Summon the Crown Prince."
"Yes, Your Majesty."
* * *
A short while later, a horse carrying a messenger galloped out of Gwanghwamun.
About half an hour later, Hyang, catching his breath, entered the main hall. After bowing to Sejong, Hyang sat down, and Sejong spoke.
"I know you have been busy with many things since last spring. I am well aware that among them, there are good results, such as the adjustment of the calendar, even though it is not yet complete. It is commendable to achieve such results at your young age."
"I am extremely grateful."
Hyang bowed at Sejong's praise.
"However, the praise ends there. There were many other things, but neither I nor the ministers received proper reports. This is different from the promise you made to me and the ministers when you first established the research institute. What did you write in the plan you submitted? You said you would thoroughly disclose the costs used in the research institute, didn't you?"
"I apologize. However, it was a matter that required maintaining secrecy…."
"Is there a secret that even I and the ministers must keep?"
"Since it was related to the defense of our Joseon, it was necessary to maintain secrecy until the final product was completed. It was to prevent any unforeseen circumstances."
"Hmm…"
Sejong, hearing Hyang's answer, fell into thought for a moment. Sejong, looking at Hyang, who was prostrate, spoke.
"I cannot continue to allocate the budget based solely on your word, citing secrecy. Even if it is an intermediate process, it needs to be reviewed. We must avoid wasting precious funds on futile endeavors. Therefore, I will conduct an audit of your activities. How much time do you need to prepare?"
Hyang, after a moment's calculation, answered.
"Please give me five days."
"Very well. I will conduct a thorough audit after five days."