Not even powerful Lifeseizers could directly consume demon cores.
After all, demonlings were filled with demon energy. When heterogeneous true energy such as that came into contact with one’s own true energy, it would be like fire and water. The violent reaction could crush one's bones and transform one's flesh into ash.
Some Lifeseizers dissolve demon cores with true energy and then use them to bolster whatever weapons or items they used in their cultivation. Others would use pill furnaces to refine them into spirit medicines.
To directly consume them like Yang Qi was simply unheard-of.
However, Yang Qi had the outrageous power of the Hellfire Crucible, which could easily convert heterogeneous true energy into something he could use.
It was something that would make him almost invincible to opponents of his own level.
In fact, that was one reason why he had been so confident in challenging Chu Tiange to a fight to the death.
He fed one demon core after another into the Hellfire Crucible, melting them into something that was useful to his cultivation.
‘Reverse the quintessence, cultivate the re-refined!’
In fact, he was converging the true energy inside of him into quintessence vitality.
Most energy artists changed life force quintessence into true energy. But Yang Qi was doing the opposite. He was taking massive amounts of true energy and changing it into life force quintessence.
And then, he poured all of that life force quintessence into the twenty-first particle within him.
After being bombarded in such fashion, the twenty-first particle reached the point of being unable to remain asleep. As it woke, the aura of an ancient megamammoth began to course through Yang Qi.
It felt like being bathed in true energy. At the same time, a lava-like energy field sprang up around him, locking down his room and even forcing the formation of spirit convergence to stop functioning.
Yang Qi suddenly flew out of the window, moving with incredible speed and simultaneously reining in all of his true energy fluctuations.
Outside, he took advantage of the darkness of night to unfurl his Fiend-Devil Wings and then blur into motion, vanishing without a trace.
Now was the moment in which he would break through to the Lifeseizing level.
However, he didn't want to make a scene in his room in the Demi-Immortal Institute, lest the powerful experts there catch on to his secrets.
He flew through the air as fast as lightning, traveling for a full two hours before dropping to the ground and proceeding along on foot. Eventually, he found himself in a remote, unnamed coastal region roughly five thousand kilometers away from the institute.
He could see the waves of the sea pounding the shore, and there was even water vapor in the air. Up above, a bright moon shone down on the lands below. 
‘This should work. The boundless, uninhabited ocean is the perfect place to break through to the Lifeseizing level.’
With that, he flew out over the ocean until he found a rather desolate reef, void of vegetation, and just barely above the surface of the water.
It was almost questionable whether the reef could survive the onslaught of the waves for much longer, and yet Yang Qi didn't seem bothered by that at all.
Looking up at the moon, he took a deep breath, circulated his energy, and let out a long piercing cry. Out here, he could be as loud as he wanted.
That particle within him erupted, sending out a flow of energy that calmed all of the ocean water within ten thousand paces.
Furthermore, the intense heat of the true energy caused steam to rise up as the water evaporated.
Nothing seemed capable of standing in the way of this energy flow.
The twenty-first particle was awake, and the power of that ancient megamammoth thrummed in his muscles, blood vessels, bones, and meridians, all of which seemed as tough as metal.
He was no longer human, nor of the Demonfolk. Instead, he was now becoming more like a god.
There was no demon energy inside of him, only the energy of a god-spirit.
Human energy was warm and active. Demon energy was strange and powerful. Devil energy was cruel and vicious. But the energy of gods was holy and noble, surpassing anything and everything else.
Now that Yang Qi had the power of twenty-one ancient megamammoths, it was time for him to break through. His thoughts and his mind were now far more powerful than before.
In fact, he could sense millions upon millions of nodes of vital energy in the air around him, things which were not visible to the naked eye.
By absorbing that vital energy, and combining its power with the particles inside of him, he could seize life from the heavens, and advance his cultivation. In the Lifeseizing level, one seized the minuscule quintessences of the vital energy of heaven and earth, then infused it into one’s fleshly body to bolster its life force.
As Yang Qi sent his thoughts out into heaven and earth, he felt like his mind and even his soul were being torn apart by vital energy.
Seizing life from the heavens was no simple matter! When reversing the ordinary course of one's life, it was only natural that there would be some opposition from heaven and earth. After all, it involved inserting one’s mind into the vital energy of heaven and earth, which would do its best to destroy the intruder.
And that was exactly what was happening right now with Yang Qi.
Unfortunately, it would be ten times more difficult for Yang Qi to achieve his breakthrough than it would be for ordinary energy artists. Perhaps even a hundred times. The resistance from the vital energy of heaven and earth would be even more severe. In fact, at the moment, Yang Qi was like a helpless child in the middle of a violent storm, with a tornado looming over him.
Boundless streams of vital energy swirled around the reef, pouring into him, causing him to tremble as his skin stretched on the verge of ripping apart.
Soon, glittering, dark golden blood began to ooze out all over him.
‘Crap!’ he thought, as he realized the level of danger he was in.
Throwing his head back, he let loose another long cry. ‘Don’t tell me that I actually don’t have what it takes to reach the Lifeseizing level? Am I lacking life force quintessence? Will I be unable to seize life from heaven? Fine. I guess now is the time to see how terrifying godly-class energy arts really are!’
Suddenly, an enormous demon core appeared from within his thumb-ring, pulsing with corpse energy, and a most sinister life force quintessence. This was none other than the demon core of King Huaiyin, a thousand-year-old corpse king.
Within that demon core was the cultivation base quintessence of a Lifeseizer.
And now that he was trying to reach the Lifeseizing level himself, Yang Qi decided to consume it.
He crushed the demon core, causing corpse energy to belch out. As it streamed into his sea of energy, and the Hellfire Crucible, the intense heat caused the corpse energy to be transformed into pure life force quintessence.
The full power of the demon core was now at work within him.
The cracks which had been spreading out on Yang Qi’s skin healed, and his blood began to pump vigorously. Even his bones began to shine a dark golden color.
As of this moment, Yang Qi looked like a god descending from heaven. Waving his hand, he caused a whirlpool to spring up in the seawater, which rapidly became something like a tornado, linking to the clouds above.
“Let summer lightning fall!”
Rumbling could be heard within the clouds, and the flash of lightning was visible as rain began to fall.
Within moments, the entire area around Yang Qi had turned into a massive storm.
This was the ability to manipulate meteorological phenomena: transforming water into clouds, transforming clouds into rain.
“Seize life from the heavens!” Yang Qi roared. As his thoughts grew more focused and powerful, the various streams of vital energy began to separate into distinct kinds: gentle, soft, filled with life force, mighty, deathly, desolate… and even some that seemed like sword energy. There were millions upon millions of types of vital energy, and sometimes it was difficult to tell the difference between them.
Some of the gentle vital energy entered him, and at the same time, some of the desolate, deathly vital energy was expelled.
Yang Qi began to float up into the air, the heat radiating off of him being so intense that the reef below him began to melt, sending rivulets of molten liquid into the ocean and causing steam to billow up, and even killing some of the nearby sea creatures.
It was as if energy from hell itself were filling the area.
Yang Qi began to spin, causing the burning energy to rotate, and sending even more steam rising up into the sky.
Strange transformations were already beginning to occur within him, down to his bones and organs. The membrane beneath his skin was turning cutaneous. At the same time, a holy and magnificent aura began to swirl around him, and his heart began to pound.
Thump-thump. Thump-thump! Thump-thump!!!
His energy pulse and his heartbeat formed a resonance that rumbled with thunderous intensity.
His heartbeat was like a heavenly drum, and his energy pulse was like furious thunder!
All of it indicated that the very substructure of his life force was changing.
At the same time, mysterious streams of life force began to emerge from the air and enter him, heading straight toward the sleeping particles.
Instantly, a twenty-second particle woke up, then a twenty-third, a twenty-fourth… all the way to the twenty-ninth.
His energy was now as tough as iron, and at the same time, as soft as water.
This was the Lifeseizing level!
The sea water around him crashed and exploded as the power of twenty-nine ancient megamammoths pushed him the final distance.
He was finally in the Lifeseizing level!
Hey everyone, I think that by this point, the author has settled into the usual rhythm of writing a web novel. By that I mean, I’m noticing more and more repetition to fill word count quotas. I’m going to be cutting as much of that repetition as possible to keep the chapters tighter. Sometimes that will mean just leaving out entire lines that are slight variations on things already stated. Sometimes it will mean combining two slightly different sentences into one. I don’t think it will significantly reduce the length of the chapters, and should make the story a bit more smooth.