"Fiend qi?" An Jing immediately put up his guard. He tried to sense his dantian ocean but didn't notice anything amiss. Even so, he trusted Yvelbane. "My senses aren't that sharp yet. Do I have to circulate Sword of Tranquility?"

"It's not just enough to circulate it, but I can help you. Close your eyes and visualize lending me your vision."

An Jing did as he was told. A rusted broken sword manifested within his sea of consciousness. Then, he suddenly felt a chilling pain at his forehead as if a tiny sword was lodged into it, burrowing a slight hole. Then, there was a sword flash of silver and white. An Jing could finally "see."

Everything around him from the glass platform, wooden figure, bed and rest of the room faded into obscurity, leaving only a faint white-green qi vein beneath him. The vein stretched out endlessly into the distance and fused with a much larger flow of green. The vein network seemed to spread far and wide into countless tinier streams. This was the spirit vein that was connected to his room, which was linked to the terrestrial veins of the black market's spirit spring.

Yvelbane had greatly expanded his senses and perception, allowing him to block out mundane things to focus on the flow of the terrestrial vein. The ability to sense the flow of qi was incredibly important as far as geomancers or spirit-vein masters were concerned, which saved them quite a lot of trouble and unnecessary mistakes. It was akin to directly observing qi with just sight.

Just like that, An Jing was able to see the fiend qi that Yvelbane mentioned. Unlike the dense fiend qi that he could rudimentarily sense in Void Embrace, this feeble trace of fiend qi was incredibly thin and barely detectable within the larger flow. When An Jing was done cultivating, the fiend qi began to fade even more. If not for Yvelbane's sensitivity, it would have remained undetected. Trace amounts though it was, the fiend qi was present all the same.

The sudden void sensation in his body caused his eyes to snap open, interrupting his spirit sight. Yvelbane's techniques might be amazing, but they're far too advanced and consume spirit energy. That's why it recommended Evenstar Ivory Divine Seal to me so that I can generate my own spirit qi as soon as possible.

"It doesn't seem like the black market is up to anything bad," An Jing said. "Instead, this might just be an innate characteristic of Skysource itself."

An Jing was no longer blindly ignorant to the nature of these two worlds. He was well aware that Skysource was filled with fiend and tribulation qi thanks to the world calamity. Even terrestrial veins were no exception. Only a few major spirit-vein cities and smaller settlements in the entire world still had access to unpolluted spirit veins, which was the only lifeline that sustained the qi-cultivation civilization.

The land that the black market occupied, however, had been corrupted to begin with. It was only due to the purification efforts of the factions that ran the black market that the spirit veins were made usable, but even that wasn't enough to completely excise the fiend qi.

"I understand now," Yvelbane said contemplatively. "This is why souljades are so precious in this world. During the later stages of qi cultivation, one has to nurture the consciousness and develop the mind.

"Clear lucid breath is also required to nurture the purple mansion, and it is only obtained through refining pure spirit qi. If Skysource was similar to Void Embrace before the world calamity, pure spirit qi wouldn't be hard to collect. Any cultivator would be able to foster clear lucid breath by silently cultivating for a hundred days. With an artifact or formation's help, one would only need ten days or so."

It clicked in An Jing's mind. "But the corruption of Skysource made pure spirit qi much harder to procure, making it hard to generate clear lucid breath, right?"

"It's still possible, but not without great difficulty," Yvelbane said, hesitant to conclude. "The fiend-qi concentration in this spirit vein, for instance, isn't a huge problem. The body can naturally expel it like any waste qi. But if someone who's nurturing their purple mansion accidentally allows traces of fiend qi into it, the foundation they build will be incredibly vulnerable to going haywire. Even if they manage to successfully build one, it will be of subpar quality. Heavenly fiends might be able to exploit it from outside.

"An Jing, you have the Spark and are born with sharp senses. Not to mention, you're training in both the martial and immortal cultivation paths. As such, your mind will be much stronger than those of average cultivators. Yet, even you had a hard time detecting the fiend qi. How could normal cultivators possibly be sure that the qi they have access to is completely free of fiend qi? Without the guidance of a master, their only choice would be to rely on a natural source of the purest spirit qi for cultivation, in other words, souljades."

Yvelbane also figured out something else. "I had been wondering why there are very few intermediate cultivators even though everyone in this world cultivates. It turns out that with most of the terrestrial veins corrupted, cultivators have to be exceedingly cautious, resulting in slowed progress. Souljades are the only thing that can speed up their cultivation and they're produced by the only three remaining unpolluted great spirit veins, which the major sects no doubt have complete control over.

"The latter stages of mind cultivation doesn't just involve establishing the foundation, but also the purple mansion. If the production of souljades is strictly controlled and managed, most cultivators would be stuck in the early stage, even if basic cultivation is widespread and available to everyone.

"Even if there were some rare geniuses that could reach the latter stages without relying on souljades, they would be quickly identified and absorbed into those major sects. This might be one way that the major sects of Skysource use to filter out talented cultivators. They're also able to maintain societal stability with this."

"Indeed." It made lots of sense when An Jing thought about it. "You really thought it through rather extensively. I thought cultivators of the ancient times wouldn't involve themselves in mundane things like ensuring the stability of their reign."

Yvelbane calmly said, "There are cultivators of all sorts from my era. Layfolk societies were basically places where we picked our crops. The recruiters of those sects had many ways to filter out people and I only have a passing understanding of them."

"So that explains why souljades are only used sparingly. They're basically guaranteed ways to reach the peak of qi cultivation in the world of Skysource."

"That's right."

An Jing nodded earnestly. "Two pieces of souljade won't really affect the whole market. But if I bring more than ten at once, the black market might take notice and I'll be in trouble. Fortunately, they only think I'm some badlander who happened upon an uncorrupted vein. I should still be able to trade more in, but I have to be careful about how much I bring."