A series of percussive sounds resembling war drums echoed from Xing Chen’s body as his chest heaved violently. Terrifying cracks snaked through his skin, presenting quite the macabre sight.
Endless starlight streamed down on him, forming a protective shield against the giant, powerful lungs while the organ continued breathing.
The lungs were a formidable imitation of the world’s lungs. Though Xing Chen’s body was sturdy, he was still a returned void realm cultivator. Having him devour the lungs was akin to a snake swallowing an elephant—no, a more appropriate analogy would be an ant ingesting a dragon.
If not for the cosmic energy around him and the power of the three great connate treasures, he would’ve exploded instantly.
“No wonder Violetgrave said that only by possessing the Tome of Life and Death am I able to refine the lungs.” Lu Yun fixed his eyes upon Xing Chen with a slight frown.
The Tome of Life and Death did indeed exist in Lu Yun. While it protected his body, though, it didn’t protect his replica. If Lu Yun devoured the lungs himself, the book would’ve emerged and refined the lungs immediately.
To protect his replica, he would have to activate the Tome of Life and Death himself, which was something he couldn’t yet do, given his level of strength. In other words, most of the time, the book protected its owner by reflex. What little power Lu Yun could generate by activating the book was too weak to even matter.
“I hope the three connate-grade treasures will be able to suppress the lungs.” Lu Yun took a deep breath and closed his eyes, his consciousness plunging into his replica.
Thud! Thud! Thud!
Bam! Bam! Bam!
The lungs released increasingly greater power within Xing Chen’s body, and the ominous rumbling now resembled thunder more than mere war drums. Even the air in hell was affected, flowing in rhythm with the lungs’ breathing.
Many of the Infernum and newborns in hell fell under its influence as well. Their breathing adjusted to be in sync with the lungs.
“Hm? Their breathing...” Lu Yun paused. “It seems capable of strengthening the organs and the muscles! Is this… a breathing method?” Inspiration flashed through the darkness.
“Most immortals today focus on tempering their nascent spirits and inner energy. Very few put in any effort to train their bodies. Therefore, immortals are usually physically weak—much more so than monster spirits, demons, and divines.
“The immortals of the Primeval Era were in a better condition, since they at least had solid foundations. Immortals of today, though, are born flawed. Even after ascending to immortality through the void realm, their constitutions remain a great weakness!”
Lu Yun recalled the many immortals that’d been devoured by yin spirits before they could even make a move during the invasion in Azure Province. Even dao immortals had been chomped down on before they could fight back, once the crimson spirits closed the distance.
“Their weak physique is the problem! The rhythm at which the lungs breathe can move the organs and train the muscles and bones, improving one’s physical prowess!” As Lu Yun breathed in unison with the lungs, all of his muscles and bones began trembling slightly in response to the training.
“It really is a breathing method!” He cracked a smile. “It doesn’t matter if it’s not an effective training method yet, since it isn’t part of a complete system. Once my replica refines the giant lungs, he’ll be able to perceive the complete system and create one, or even many, breathing methods, thus giving birth to a new cultivation path!”
However, things weren’t looking too good for this new cultivation path at the moment. Xing Chen’s body had bloated like a giant balloon, and it looked on the verge of being burst by the giant lungs.
The overwhelming might of the organ had pierced through the cosmic power. With the Tome of Life and Death in his hand, Lu Yun summoned hellfire in an attempt to control the giant lungs.
“Thankfully, the lungs are damaged. If they were whole—” he cut himself short.
If the lungs were intact, Xing Chen would’ve exploded and died the moment he devoured them. Even in their damaged state, the lungs were incredibly powerful.
Bit by agonizing bit, Lu Yun lost his control over the replica as the latter inflated.
“He’s gonna burst.” Lu Yun smiled wryly. Qing Yu gripped his hand tightly, her expression nervous and her forehead covered in sweat. She’d been keeping a steady hand on the Cosmic Eyes and Cosmic Skycarver, but she was running out of strength.
A tremor passed through hell as a flash of dark light scattered the surrounding cosmic power. The Cosmic Sea returned to its form as a scroll of faint silver and drifted back into Qing Yu’s hands, along with the eyes and blade.
Another stunning explosion sounded out before Lu Yun and Qing Yu could react and a giant coffin suddenly appeared over Xing Chen’s head. Black light cascaded from it and enveloped Xing Chen.
In an instant, the area was flooded with black.
“That...” Qing Yu widened her eyes at the Enneawyrm Coffinbearers, shaking her head in disbelief. “That’s the coffin that dragged the lungs into hell.”
“I don’t know what it is, either,” Lu Yun said with a wry smile. “But it often shows up and solves problems I can’t solve myself.”
When he’d encountered the Nine-Phoenix Casket in the Sword Barrow, it’d been the Enneawyrm Coffinbearers that’d tamed the casket and brought it into the netherworld as well.
Under the influence of the black light, the giant lungs in Xing Chen’s body slowly assimilated and modified his body, creating yin and yang organs.
A metallic sound rang from Xing Chen, followed by surging metallic brilliance. A keen presence billowed out from him, depicting him as the greatest sword in the world.
“Hah—” Xing Chen tipped his head back and howled at the sky, sending out a sharp metallic energy from his mouth.
“That’s connate yang metal energy of the Mastery of the Five Elements!” Lu Yun’s eyes lit up. 
That death art could summon the power of the five natural elements out of nothing, and Xing Chen could now control the attribute of metal!
“Natural yang metal energy is one of the keenest energies in the world. Even incorporating a strand of such energy will transform a man-made treasure, enabling it to rival a connate-grade one! That’s what permitted the Sugato Sword to become the greatest man-made treasure, capable of cutting down connate-grade treasures!”
Yin wood of the east, yang metal of the west, yang fire of the south, yin water of the north, and yang earth of the center were the greatest elemental powers in the world. However, very few throughout the history of the world of immortals were ever able to wield such power.
The Azure Dragon King’s Yi Wood Cleansing Thunder was an application of yin wood.  Apart from him, the other four divine kings hadn’t developed the same mastery over their corresponding elements. That was why the Azure Dragon King had been the most powerful among the four cardinal tribes, and why it’d been the only divine king to survive the divine downfall.
Lu Yun didn’t expect Xing Chen to be able to tap into the power of yang metal with the Mastery of the Five Elements straight after incorporating the lungs. That was something he himself couldn’t yet do with the death art.
There's a lot more personality stereotypes having to do with yang metal that I didn't put into the reference note, much like how western astrological signs have certain personality stereotypes in Chinese culture. Yang metal folks are strong warriors and are all about doing and execution. However, this only happens with a heavy dose of fire. Without the fire attribute, yang metal folks can easily become very lazy.