The Bone Child, a small bony crow, stayed on the ground for some time. It wasn't moving at all, but Cao Yun could tell that it was somehow looking all around. Considering that it had no eyes and no flesh at all, it was using other senses. Honestly, Cao Yun himself wasn't sure what those senses were, but he could make an educated guess. Most likely, they were related to his own spiritual senses. Of course, instead of using an actual soul, it was the Death Energy within the Bone Child that acted as spiritual senses.
What cultivators called spiritual senses were more or less an expansion of their own soul outside their body. Of course, anything could play that role. Moreover, Death Energy originated from a soul, a Corporeal Soul. As such, it wasn't completely outlandish. Thus, Cao Yun spread his own senses. As he felt disturbances around himself, he was able to finally perceive the form of spiritual senses used by the Bone Child. It was incredibly faint and dim. If Cao Yun had not had sufficient understanding of the Dao of Death, he would have never been able to feel it at all.
This was a direct application of 'See Through the Mud'. For several hours, Cao Yun studied the tiny variations within this Death Energy. In fact, he couldn't even tell if most of those variations were real or simply came from his lack of sensitivity to Death Energy. In order to improve his perception, Cao Yun made sure to leave his body completely open. At the moment, Cao Yun had almost no defenses at all against an attack. To be fair, his flesh was so resistant that the Bone Child would not be able to even damage his most superficial skin. Besides, the Black Heart Flame was still surrounding them, so no attack could come from the outside either. Cao Yun was safe enough to cultivate as he pleased.
After enough time had passed, the Bone Child seemed to grow more and more impatient. Indeed, its head started to move around a little bit, even though it wasn't necessary for it to perceive its surroundings. Nonetheless, Cao Yun didn't react at all. He kept on observing the Bone Demon as well as the movement of the Death Energy around it. Slowly but surely, the Bone Child seemed to focus more and more on the Black Heart Flame. After all, it contained Death Energy and Bone Demons, which it needed to cultivate. Of course, it was Death Energy under Cao Yun's control, but the Bone Child didn't need a lot of it.
At first, the Bone Child focused some of its senses on the Black Heart Flame, studying it. Sensing no reaction at all from Cao Yun, it became more and more brazen. At some point, it finally moved and walked toward the sphere of flames surrounding them both. The Bone Child poked the flame with its beak. It was extremely fast and immediately retreated, scared. Seeing no negative effect, it tried again and again. Very small traces of Death Energy began to enter the Bone Child. Honestly, Cao Yun was quite happy with this development. After all, he wanted to observe a Bone Demon in action, not just study an inanimate object. So long as it wasn't a threat, Cao Yun wouldn't act against the Bone Child.
Cao Yun was still observing the changes in the Death Energy around the Bone Child. However, he changed his approach and decided to focus his perception on how the skeletal crow was absorbing the Death Energy from his Black Heart Flame. If he had wanted to, Cao Yun could have stopped it since he was in control of the Black Heart Flame, but Cao Yun was allowing it. Even if the Bone Child kept at it for months, the Black Heart Flame would barely be affected at all.
At this moment, Cao Yun was working on his 'Death Reeling', his ability not to sense but to actually affect and control Death Energy. By perceiving how the Bone Demon was doing it, Cao Yun was hoping to improve his own ability. Unlike the Bone Child, Cao Yun was working on a strand of Black Heart Flame within his own body. As an Exalted Demon, feeling it in his flesh was making the process faster. Besides, this wasn't his Soul Embryo but his Demon Soul doing the feeling. Since his Demon Soul was quite literally his own Po, and since his Po was obviously related to Death Energy, it made Cao Yun's progress faster. Faster didn't mean that his progress was fast, just that it wasn't as slow as it could have been. Cao Yun himself had a hard time knowing whether he was improving or not. However, he was sensing enough changes that he kept at it.
After sufficient time had passed, the young man began working on 'Living Death'. At this point, Cao Yun was really getting closer and closer to the limit of his knowledge and perception. 'Living Death' was the last step he could claim to have really understood. Within his Demon Soul, Cao Yun isolated a tiny fraction of his own Po, an amalgamation of several parts of his seven Turbid Demons. Then, he carefully turned it into Death Energy while staying alive. As it happened, Cao Yun saw that the Bone Child reacted to it. For a split second, the Bone Child seemed interested in Cao Yun.
Until now, the Bone Child had completely disregarded Cao Yun. After all, Cao Yun had not acted at all, he was just observing. But the Bone Child seemed to actually understand how dangerous Cao Yun was, most likely on some intuitive level. Indeed, the Bone Child appeared to be as intelligent as a regular crow. It didn't seem stupid at all, but it lacked human intelligence. That interest in Cao Yun was fleeting. Of course, Cao Yun couldn't know what it was thinking, or if it was thinking at all, but the Bone Child had probably realized that whatever it had sensed was completely out of reach, while the Black Heart Flame could be devoured.
Now that Cao Yun had turned a small part of his own Demon Soul into Death Energy, he worked with it to improve his mastery over Death Energy. When he was confident enough, he decided to try out an idea. He took his own Death Energy out of his body, pure, without anything else mixed in it. Then, he focused on compressing it right in front of him. Pushing his mastery over Death Energy to the limit, Cao Yun began to work on 'Soul Chains'.
The point of 'Soul Chains' was to materialize chains made out of Death Energy that could then attack one's soul directly. However, Cao Yun wasn't trying to create a chain or even any weapon of any kind. In fact, Cao Yun was trying to build something much simpler and smaller. He knew that enough Death Energy compressed with enough force over long enough periods of time could produce what he had in mind. Hopefully, he would be able to produce it himself, too.
As he was compressing the Death Energy, it became harder and harder to perceive all the intricacies within. As a consequence, it also became harder to control it. In other words, he was pushing his 'See Through the Mud' and 'Death Reeling'. However, he didn't have to focus on his 'Living Death' at all, for the moment. Finally, the Death Energy became so compressed that even the Bone Child lost interest in the Black Heart Flame and only observed Cao Yun's experiment. In fact, it seemed to lose interest in anything else. It was as if only Cao Yun and the Bone Child existed in the universe. Both of them were strangely engrossed in this experiment.
Right in front of Cao Yun, a small white sphere appeared. Cao Yun could tell that he was increasingly close to his purpose, but he was lacking something. Honestly, it was incredibly frustrating as he could almost touch his goal, but his finger couldn't quite get there, he was just gently grazing the surface, but couldn't grab it. That being said, he didn't let his frustration get the better of him. After all, even failures were interesting. In fact, it could be argued that failures were often more interesting as one could learn from them.
As Cao Yun was almost ready to give up, the Bone Child got closer and closer, jumping toward the young man because it couldn't fly in such a small space. Cao Yun's first instinct was to push it away, but he stopped himself. Clearly, the Bone Child was going to interact with his own Death Energy, so he wanted to know what it would do. The moss on the bones of the crow began to dwindle and wither even more. The crow was sucking Death Energy and Evil Qi out of it. Then, it breathed it out on the white fragment in front of Cao Yun. Under the effect of the breath of the crow, Cao Yun felt that the process that had seemed to stop suddenly began anew. Sadly, it wasn't extremely fast, but it wasn't halted anymore.
Strangely enough, Cao Yun and the Bone Child worked together for several hours until finally they achieved their common goal. Right in front of Cao Yun was now a white phalanx. The young man had not tried to influence the shape at all, but he had tried to materialize his Death Energy. If he had influenced it, he might have created chains or various weapons. Without any influence from Cao Yun, it had most likely taken on an appearance based on its origin. Indeed, this Death Energy emanated from Cao Yun's own Po. Honestly, Cao Yun didn't want to check out whether this phalanx could be similar to one of his. The Bone Child was so excited, it almost looked alive, jumping around, chirping as best as it could. If it had vocal cords, it would have been singing.
This phalanx was completely under Cao Yun's control. At this point, Cao Yun could actually claim to have mastered 'Soul Chains'. After observing how the Bone Child had helped him and factoring in the experience he had had a few days ago, Cao Yun was certain that he could actually manifest his own Po into Death Energy constructs. In a sense, Cao Yun had almost mastered half of 'Death Verses'. And he planned on actually mastering half of it very soon.
Without any delay, he wanted to work on 'Macabre Dance'. This was the reason why he had taken out this Bone Child. After all, Bone Demons seemed to be natural occurrences of what 'Macabre Dance' explained. As the name suggested, 'Macabre Dance' was about making dead bodies dance. Of course, the goal wasn't actual dance. Using Death Energy produced from one's own Po, a cultivator could infuse a dead body with a form of life in order to animate it. It wasn't about bringing a corpse back to life, but more or less using it as a puppet of sorts. Certainly, it was more complex than that. At the end of the day, it was a form of necromancy.
The simplest way to work on this 'Macabre Dance' wasn't to actually imbue a dead body with Death Energy. Cao Yun had reasoned that the best training method was to learn how to control a Bone Demon. Now that the Bone Child had helped Cao Yun produce this phalanx, it wasn't wary of the human at all. Maybe the Bone Child even saw Cao Yun as another Bone Demon, an ally of sorts. Honestly, it was impossible to tell. However, it seemed much more lively and even a bit affectionate. As such, Cao Yun didn't need to convince it to take the phalanx.
The Bone Child took the phalanx so graciously offered and literally began to eat it by poking it over and over again. It was minute, but some of the bone dust slowly increased the mass of the crow. Of course, a simple phalanx didn't make much difference, but Cao Yun was observing it with such precision that he could see the small changes. It would take a lot of time for the Bone Child to become a Bone Warrior. That being said, it was clearly on the road to cultivation.
Through the Bone Child's action, Cao Yun didn't need to actually imbue the Bone Demon with his Death Energy, it was swallowing it willingly. But at every single moment, Cao Yun made sure not to lose his connection with it. He could perceive every strand of Death Energy, but he didn't exert any control on them at all. When the entire phalanx had been devoured and even every tiny fragment absorbed by the Bone Child, Cao Yun could see a constellation of points within the skeleton of the crow. The young man's Death Energy was imbued throughout the body of the Bone Child.
It had been really fun to sense how his own Death Energy moved around. In fact, it allowed Cao Yun to understand the physiology of the Bone Child in much more detail. Now was the time to perform 'Macabre Dance'. The Bone Child wasn't expecting it at all, but it felt a sudden pull. Cao Yun's Demon Soul was acting upon his Death Energy trapped within the body of the Bone Child. With his current strength, Cao Yun could have just ripped it out of the skeleton, but he didn't want to destroy the Bone Demon.
By the time the Bone Child understood the threat, it was too late, Cao Yun had the creature on a metaphorical leash. Cao Yun's Death Energy spread. It became thinner and more diluted, but it also spread throughout the entire body of the Bone Child. Although the Bone Demon tried to fight back, it couldn't do a thing. Cao Yun's Death Energy connected with tiny traces of the Black Heart Flame the Bone Child had absorbed. Cao Yun also sent his own Qi to take over the Evil Qi circulating within the Bone Child.
Before long, Cao Yun could control the entire bone structure of his dead avian friend. Now, the Bone Child was no more than a puppet. Although it couldn't be called 'Macabre Dance' because Cao Yun had not animated a corpse from scratch, it was very close to it.
At first, Cao Yun wondered if he would just control the Bone Child like a puppet. Thankfully, he realized that it was different from his expectations. The Bone Child felt like an extension of his own soul, while being independent. In other words, it could act on its own, it had its own form of intelligence, but it was completely subservient to Cao Yun even without giving it any order at all. Whatever will had been animating the Bone Demon had now been erased and replaced by Cao Yun's own will.