Cao Yun had access to a lot of information. Honestly, the most useful knowledge came from Cleansed Asura's memories. Cleansed Asura had been studying various Dao and had literally entered the God-Monarch realm. Unfortunately, he had been struck and almost killed after entering this realm. Even he had not been able to see his opponent. However, it was the very first realm outside his own he had visited. For a God-Monarch, entering another realm was always a dangerous endeavor, especially for the very first time. Despite those circumstances, it was clear that whoever had been able to slay him was either a God or also a God-Monarch. Considering that a God could live for hundreds of millennia, this cultivator was most likely still alive. Anyway, this was a problem for later.
Using some books he had obtained from other sources, and memories and thoughts from other souls, Cao Yun reviewed everything he knew about the study of the Dao. The actual Dao was not something anyone could easily access. In fact, even describing what the Dao was was difficult in itself. Most cultivators understood it as a universal concept imbued within absolutely everything: living objects, inanimate objects, but also within concepts, within time and space, within souls, within minds. Absolutely every single thing in existence was permeated by the Dao. From that point, cultivators all had widely diverging views on its true nature and even on its characteristics.
For most cultivators, the Dao was a concept, not a being, it had no ego, no thought, no sentience. For others, it was pure consciousness despite a lack of personal ego or identity. In fact, almost everyone would ultimately come to the conclusion that the Dao was unknowable. The Dao that could be described wasn't the Dao. The Dao that could be understood wasn't the Dao. As such, cultivators extended the concept of the Dao to a smaller part of reality. While the Dao was the first concept from which everything else derived, the smaller Daos were the laws of reality that had emerged from it. They were seen as aspects of the Dao. By studying them, one could slowly build up one's comprehension of the actual Dao.
In a sense, the Dao itself was often understood or simply seen as the laws underlying all of reality, from the most concrete to the most abstract and conceptual. The Dao had created the Wuji, the Pure Void. Everything was One. From the Wuji emerged the Taiji, the first principle of differentiation. From it were born the two opposite aspects, Yin and Yang, the first duality. By their opposition was born the first movement. As the movement put the two opposite principles in motion, they created four: lesser Yin, lesser Yang, great Yin, and great Yang. Finally, they could form the Eight Trigrams, which spread in all Eight Directions as they emerged from this movement. Then, those Eight Trigrams interacted with each other and gave birth to all ten thousand things.
Although it seemed clear on the surface, Cao Yun had a hard time wrapping his head around all of this. First of all, the characters used had many different meanings and could all be understood in very physical or metaphysical ways. In other words, it was an absolute mess. Even a simple sentence could have given rise to thousands upon thousands of books that couldn't even exhaust all possible understandings.
Instead of losing himself in philosophical debates that would never be able to get to any useful point, Cao Yun actually wanted answers. So he decided to work with what he could. The most common Dao studied by cultivators was the Dao of Fire. It was useful in cultivation, in alchemy, and in martial arts. There was no reason for a cultivator not to study it except for time. Some cultivators skipped it or didn't spend much time on it because they were busy studying other Dao. Sometimes, they simply were better with other Dao or had more affinity, more comprehension of them than the Dao of Fire. This wasn't Cao Yun's case at all.
Cao Yun had his Black Heart Flame, the Dao Seed of his Solar-Orchid Flame, and even the Rune of Fire that had merged with the Dao Seed. Technically, one could say that he had already studied the Dao of Fire. But it wasn't actually the case. Unfortunately, it was impossible to pass on one's knowledge of the Dao to someone else. However, it was possible to capture small parts of the Dao in various ways so that one could study it with more ease. In a sense, it was the raw material Cao Yun could observe to understand the Dao of Fire better and faster. Within all the knowledge of Cleansed Asura, Cao Yun found the journal that seemed the most intuitive to him.
Even Cleansed Asura didn't have the name of the author, unfortunately. From what Cao Yun read, it was obviously an alchemist. After all, he was making comparisons and images using alchemy more often than not. Moreover, he discussed how the principles of the Dao of Fire could be used in alchemy. Unlike some authors, he focused more on free expression than on rigid systems. Studying the Dao wasn't like martial arts, there weren't any techniques to learn. Techniques could be derived from knowledge, like 'Death Verses', but the Dao itself had to be separated from the use of the Dao.
The unknown author had named his journal 'Red Calm on a Sunny Day'. To be honest, Cao Yun wasn't sure if something had been lost in translation or not. Since he had no name for the alchemist, Cao Yun decided to call him Red Calm. Reading Red Calm, his first point was that one had to be able to form what he called Fire Silk. He explained that many cultivators were just trying to produce more powerful or bigger flames. This was a mistake. Creating an out-of-control fire was easy, anyone could do so, even mortals. Cultivators weren't trying to lose control, they wanted to understand the Dao of Fire, not burn all of existence to prove how powerful they were. By creating a fire that they couldn't control, they would just prove how foolish they were.
If one could control fire to the point where they were able to create Fire Silk, then they wouldn't lose control under any circumstances. As Cao Yun read, he understood why Red Calm was so confident.
Fire Silk was the idea of a single thread of fire, so small that it was invisible to the naked eye and so long that it could circle the Piaolu planet several times. Of course, the thread would be folded upon itself so it wouldn't take a huge volume, but its length was supposed to be immense. As for its width, it had to be thinner than a single hair and by a large margin. In fact, Red Calm's idea was to make it as thin as possible without extinguishing the fire. Even a Spirit Warrior wouldn't be able to see it with his naked eye, but would have to use spiritual senses.
There were many advantages to this training method. The first one was that it was very difficult for the cultivator to injure himself or others. Indeed, the fire was so small that it couldn't get out of control. The second one was that it forced the cultivator to absolutely focus on every single detail of the flame, increasing their affinity with the Dao of Fire. The third one was that even someone who couldn't produce large amounts of fire could start by working on Fire Silk. In fact, there was no requirement as to the type of fire. Even mundane fire from burning wood or coal would do the trick. Of course, Cao Yun would begin with his Black Heart Flame. He hoped that working on this fire that contained Death Energy, it would help him get familiar with the Dao of Death as well.
After reading 'Red Calm on a Sunny Day' and comparing it with many other manuals, Cao Yun was convinced that it was sound. However, he couldn't know how well-suited for him this method was until he tried it. Instead of losing himself in working on hundreds of different methods that all seemed interesting, Cao Yun made up his mind and started the study of the Fire Silk.
There wasn't much indication on how to do so, except for taking a small amount of fire and slowly making it thinner and thinner. If it became thin enough, then it was necessary to progressively add more fire without collapsing the Fire Silk.
From Cao Yun's fingers, ten black tongues of fire emerged, his Black Heart Flame. Just taking his flame out of his body had an impact on Cao Yun. Without using his spiritual senses, he already felt closer and even more intimate with these flames. He could feel their heat almost as if it were the heat of his own flesh. Honestly, the feelings were very particular, and he couldn't fully describe them. The flames were a part of him, and he was a part of the flames.
For several hours, Cao Yun tried to make the Black Heart Flame thinner. Unfortunately, he didn't succeed at all. And by that, that meant that he wasn't able to contract them in the least. In fact, some of those tongues of fire looked a bit bigger. Although Cao Yun was able to control the intensity of the flames and their movement, even their form to some extent, he was absolutely unable to make them any thinner than they were.
Considering that studying the Dao could take centuries or even millennia, Cao Yun wasn't dispirited by those few hours. However, he could tell that his approach was wrong. After the first surprise, Cao Yun realized that he simply couldn't perceive the Dao. His Dao Seed barely responded. So he decided on another approach to see if it would improve the result.
While Sages used their souls to perceive the Dao, Exalted Demons used their own bodies. Indeed, their Demon Soul was their own Po, their Corporeal Souls. As such, Cao Yun took back his Black Heart Flame and sent only one surge of the Black Heart Flame directly into his Lower Dantian. Even if, somehow, there was an accident so little fire wouldn't affect him at all.
Now, his Black Heart Flame was both within his body, but also very close to his Dao Seed and even to his prenatal Jing and his Golden Fate. In other words, it was closer to a physical manifestation of his Po. At the same time, it was close to where he would have to produce his Common People's Fire.
Cao Yun kept on working for several hours on this single strand of Black Heart Flame. After three hours, Cao Yun realized that his strand of Black Heart Flame was a tiny bit longer. When he checked, he confirmed that it was also a tiny bit thinner. There was nothing impressive at all, but he could clearly tell the difference. In fact, the experience itself was different, he had a greater connection to the Black Heart Flame and could also sense his Dao Seed working alongside him.
This tiny success pushed Cao Yun to keep working and working on it. The young man completely lost track of time.
Bit by bit, his Black Heart Flame became thinner and thinner. Even after days of work, it had probably lost less than the width of a single hair, but it was definitely thinner. The young alchemist could tell that it would take years to be able to produce the actual Fire Silk. However, he also realized that his sensations were getting better and better. At first, he was truly lost. He would try to focus, but couldn't really perceive what he had to do or what he had to focus on precisely. But now, he had a rough understanding of what he had to worry about, what aspects were useful to observe. He was actually getting more proficient each time. As such, the process that had been frustrating at first had now become a game. He couldn't stop playing.
Almost a week passed and Feng Yingyue entered Emperor Weide's chambers where Cao Yun was sitting cross-legged. She saw her Dao partner covered in sweat. His body was perfectly immobile, and he barely breathed. It was obvious that he was in extremely deep meditation. Around him was a strange heat. As an alchemist, she could tell that this heat wasn't produced by his body alone, it came from deep within and was the physical manifestation of some powerful flame. After all, it was also altering the Five Elements around Cao Yun.
Although she didn't want to stop Cao Yun in his meditation, she had to. So she was extremely gentle. In fact, she didn't touch him or even talk to him. Instead, she spread her Qi slowly in his direction. It took Cao Yun several minutes, but he left his deep meditative state. Honestly, he wanted to keep working on it. For him, it felt as if only a few hours had passed by. However, he recognized Feng Yingyue's aura and knew she wouldn't disturb him without good reason.
When he opened his eyes, he saw her and felt that his body was a bit tired. Suddenly, he could feel the sweat on his skin and his clothes. It had clearly been several days. And Feng Yingyue's words confirmed it.
"Our transport is ready. We're set to depart for Baziyun City at any moment, now."
"Thank you."
Only then did Cao Yun realize that a week had passed. He had not even realized it. In the end, it was a good idea to stop working on the Fire Silk for now. He needed some rest to digest his thoughts and perceptions. Spending too much time on a single task wasn't often the most productive activity, even when it felt good. He could get lost in his own thoughts and not consider alternatives. In fact, he could get in his own way. Stopping to think critically on his progress, or simply to stop worrying and let his mind naturally wander around were great ways to achieve better results in the end. Everything was in the balance. Resting was essential, but it was necessary to work enough before resting. Stopping for too long would hinder Cao Yun, as he would have lost his perceptions before working on his Dao of Fire again.
Moreover, Cao Yun would have several months to meditate on the way to Baziyun City. After that, he would have even more time to get to his final destination, where the confrontation with Empyrean Asura would take place.