Cao Yun had indeed planned for his breakthrough into the 8th-stage Accomplished Demon grade. He had hoped to achieve that before getting into the Hongchen Kingdom, even though he had tried to mainly focus on his Qi cultivation. To be fair, he had progressed a lot and was a late 5th-stage Spirit Warrior. Cao Yun could already feel that his Soul Embryo was very familiar with his own soul. In fact, by using Cleansed Asura's 'Intimate Through Despair and Agony' technique, his own soul and his Soul Embryo had become extremely close. That being said, it would still require some time for him to be able to walk into the next stage. As a matter of fact, getting closer to forming a full Demon Soul would probably help him a lot. After all, any bit of understanding of his own soul he could gain would be helpful in the long run.
With those plans in mind, Cao Yun prepared. In the very cave he was in, there were array formations meant to both help and conceal his cultivation. Indeed, he didn't want to be discovered. Unfortunately, Cao Yun was still unaware of the seals hidden in his blood and in his Golden Fate, his very essence. Otherwise, he and Dian Mo would have already been working on getting rid of them. But by shifting his focus toward cultivation, it would take them even longer to find those out.
Since his last Turbid Demon was so closely related to Death Energy, Cao Yun decided to read some more about it. In fact, he dived into Yu Xiangling's memories. That woman had read the Holy Scripture of the Empyrean Asura, or rather of the Heavenly Demon God Da Mo. But of course, those two were in fact one and the same.
For the time being, Cao Yun had caught glimpses of those memories as he had essentially focused on array formations and seals in order to take over the Temple of Grace and Submission. But now that he had some time, he endeavored to learn everything she knew about Death Energy, Ghost Energy and Evil Qi.
What he learned was rather common at first, at least, common knowledge to him. Humans and demons were extremely similar apart from meridians and Dantian for humans and powerful blood for demons. Obviously, those caused the differences between them. In fact, the potent blood within asura was the reason why they didn't have any meridians nor Dantian. First of all, they were rather useless considering that their blood was able to nourish their entire being with Qi. But their blood, in utero, was corroding the basis of their Dantian which would have slowly developed into many meridians and vessels. Thus, it explained why humans couldn't cultivate like demons. If they went too far with blood cultivation, they could quite literally destroy their own meridians. On the other hand, demons could not follow the human cultivation because they didn't have any meridian to begin with.
Thanks to his Drop of Wrath, Cao Yun had been able to cultivate both systems. His meridians and Dantian were simply sturdy enough to resist this blood. Most likely, it came in large parts from the fact that the Drop of Wrath had quite literally remade his body when he had been killed by his family's murderer. At that time, his entire cultivation had been destroyed, but it had been a blessing in disguise.
When it came to the soul, humans and asura were identical, deva were different but Cao Yun knew very little about them. Apparently, they had something similar to meridians but more complex than humans. Their main superiority was indeed their soul and they focused on it, but even Cleansed Asura had not met that many of them and had not discovered too much about them as he had other priorities.
What was called the soul was the seat of emotions, ambitions, desires, both earthly and spiritual. It was often put in opposition to the mind that was rational, the seat of one's intellect. Without the soul to have any goal, intellect was useless. But without the mind, one's goals could never be achieved either. The soul was made of, or divided into, ten souls. Some thought they were ten aspects of the same soul while others believed that those were ten different souls interacting with each other. Cao Yun had read extensively on the matter. Seven were forming the Po and three the Hun. Now that he was thinking about it, his Demon Soul would become a second Po while his Soul Embryo would act as his Hun. Seeing things like that would probably be helpful when he tried to combine them together, which he absolutely intended to at least try.
The Hun was the part of the soul humans, and some demons, believed could survive the physical death and be reincarnated. Honestly even Cao Yun wasn't too sure about that. He had seen people's Hun leaving their body at their death, but he had no idea how it could lead to reincarnation or how one's Hun would integrate a new body. But he still believed in it. After all, even the same Hun could give rise to a different person as it would interact with the Po that mostly originated from one's essence. That meant that the Po was the earthly soul that emanated from the parents.
Those were some esoteric concerns that weren't important at the moment though. What truly mattered was that one's Po would help the body develop, then help keep it alive by creating earthly urges and desires, and ultimately would help it die and decompose. The Po was thus essential to allow the Hun to exit the body intact. If the Hun was damaged or corrupted in any way, it could turn into Ghost Energy. With enough Ghost Energy, true ghosts would manifest themselves, remnants or echoes of the dead, with bits and fragments of their memories.
On the other hand, the Po would naturally turn into Death Energy, it was supposed to in order to corrode the body and help the Hun escape. Death Energy was part of the natural process while Ghost Energy was a mistake that could occur during that process. It was clearly shown in 'Death Verses'. Indeed, the third verse of it was 'Living Death'. This verse consisted in turning one's own Po into Death Energy and back into Po. In other words, it was possible for a living being to produce Death Energy while alive and to harness it. As it turned out, this was the main reason why Cao Yun had been pushing off his breakthrough.
His last Turbid Demon was the Devouring Robber, his Po of Death. This was the part of the Po responsible for turning the entire Po into Death Energy. Cao Yun could not understand the Dao of Death before being a Sage. Indeed, a Sage could open their soul to the outside world and finally be able to see through the Dao, or at least parts of it. Even an Accomplished Demon with great spiritual senses couldn't reach such a level. However, if the phenomenon were to happen within Cao Yun's own soul, he might be able to catch a glimpse of the Dao of Death. At least, he was hoping he could.
Yu Xiangling had found a way to trap one's Hun within their dead body. Like that, the natural Death Energy would decompose the rotting corpse and sever the tether of the Hun. But with no escape, the Hun would be tortured by this Death Energy and would turn into Ghost Energy while producing more and more Evil Qi. After all, Evil Qi was just Qi that had been mixed with negative emotions, so it wasn't that different from ghosts in a sense, except for the memories.
Looking through her memories, Cao Yun realized that she had not mastered the 'Soul Chains' he was hoping to achieve. 'Soul Chains' was the fourth verse of 'Death Verses' and consisted in physically manifesting Death Energy as chains and other weapons. Even with his Black Heart Flame, Cao Yun wasn't able to manifest his Death Energy. Indeed, his Black Heart Flame was just fire with Death Energy, Evil Qi and a bit of Ghost Energy within. When he used it, he just unleashed it and controlled it but he couldn't really shape it in any other form. Being able to manifest Death Energy into physical form was extremely useful as it could create more sophisticated attacks as well as help his own soul cultivation. After all, the last stage of the Accomplished Demon realm was called 'Chaining the Beast'.
In that stage, one would create physical blood chains to subdue and tame their own Demon Soul for good. Right now, Cao Yun had similar chains but they were not physical manifestations and they mostly emanated from his Drop of Wrath and his 'Sealing the Seven Demons in the Nine Peaks'. In fact, the seed of the world tree that he had absorbed was also reinforcing those chains around his Nine Soul Peaks so they were almost physical manifestations. Still, they weren't physical manifestations of Death Energy at the moment.
What surprised Cao Yun though was that Yu Xiangling had a deep understanding of the fifth verse of 'Death Verses', 'Macabre Dance'. Thinking about that, it wasn't that strange either. This 'Macabre Dance' was about using Death Energy to control and animate dead bodies. However, what Yu Xiangling did was very different from the actual 'Macabre Dance'. In that technique, one would use their own Death Energy. What Yu Xiangling had done was to use a dead demon as a basis and add more and more Death Energy and Evil Qi from other poor victims into it. If the demon she was using as a basis had enough will, even their Death Energy and Ghost Energy would retain enough ego to harness this flow of death into their corpse. As seals were trapping all of that within the armor of the Supplicant Tyrants, they became dangerous killing machines. But if the demon used as basis wasn't strong enough, the Supplicant Tyrant would just collapse.
Looking through all her research, Cao Yun was understanding more and more about Death Energy but also Ghost Energy. At the same time, he was truly disgusted by her methods. In fact, they were even more horrendous than he had imagined. Never had she considered her 'test subjects' as conscious beings. They were just tools and materials for her experiments. That being said, she was also very aware that they were emotional beings and she had been using those emotions to make sure that her research was successful. After all, one's soul was directly connected to their emotions. Her total lack of compassion for them was paradoxically coupled with great empathy. She was able to clearly see through their emotions in order to use them against them.
Since he didn't want to get riled up before attempting a breakthrough, Cao Yun tried to remain as detached as possible. Besides, she was already dead. She couldn't pay more for her crimes.
Although he studied her memories for a very long time, Cao Yun didn't improve his understanding of 'Death Verses' by much. He did progress a little, but it was very small. To be fair, without being a Sage, it was almost impossible to catch even a glimpse of the Dao. And the Dao of Death was a very important Dao, on par with the Dao of Space and the Dao of Time. Those were major Daos that even a Sage would find difficult to comprehend. Without Cleansed Asura's notes or the Heavenly Demon God's Holy Scripture, Cao Yun and Yu Xiangling would have never even approached the Dao of Death to begin with.
Even this tiny progress was a good achievement. Moreover, simply thinking over the matter and reviewing what he already knew helped Cao Yun prepare for the breakthrough. At least, he knew what to look for during the process. Indeed, he was still hoping to develop his 'Living Death'. For the time being, he had a very good understanding of the first two verses, 'See Through the Mud' to perceive Death Energy, and 'Death Reeling' to control Death Energy just like Qi. If he could finally practice 'Living Death', he would be able to produce Death Energy from his own soul. In fact, he might be able to do so from the Drop of Wrath. So one could imagine the gain in power.
This Drop of Wrath belonged to Axiu Qian, a pure-blooded asura who had most likely reached the eighth realm of cultivation, or at the very least was extremely close to it before his death. Even now Cao Yun wasn't absolutely sure of his actual cultivation at that time, whether he had been a Heaven Traitor or a Conqueror. Although the Drop of Wrath was a mere fragment of this being, it would surely produce incredible Death Energy that Cao Yun could harness into his Black Heart Flame. Against powerful beings like Emperor Weide and the Empyrean Asura, it could become terrifyingly effective. If the Empyrean Asura was truly a part of Demon God Da Mo's soul, this could be Cao Yun's greatest trump card.
With all that in mind, Cao Yun finally turned back toward Dian Mo. The spirit was getting more and more tired with each passing moment. Keeping the Devouring Robber suppressed was exhausting.
"I'm ready. As soon as I open those array formations, begin to unleash a tenth of the Devouring Robber."
"Boy, I don't know how much I'll be able to suppress it once I unleash the beast. I'll try to keep it in check, but be extremely careful. Remember, if it consumes you and you die, I'll also be engulfed. Your life isn't the only one on the line at the moment."
Although Dian Mo's words seemed selfish, Cao Yun could tell he was just trying to push him to succeed. With someone else's life in danger, Dian Mo hoped it would make Cao Yun try even harder. Honestly, he wasn't completely wrong. But, as much as Cao Yun didn't want to cause Dian Mo's death, the life that was truly concerning him was his own sister's. If Cao Yun died, she would be slaughtered like a pig by Emperor Weide when he deemed her 'fattened' enough.
There was no way Cao Yun would fall now. He was so close to getting back home and saving his sister. After his expedition in the demon territories, Cao Yun's next destination was the Hongchen Kingdom but he needed strength. And now he was going to get it!