The Martial Unity

Project Niflheim was a domain meant to create a cold environment antithetical to beasts who couldn't handle the cold whatsoever. Fortunately, even before he got to the project, Project Muspelheim had given him several ideas.

"Convection," Rui remarked. "It's more useful for getting rid of heat than heating."

While Rui was confident that he could use it to heat the Muspelhein domain, it was even more naturally useful in the Niflheim domain. He could use convection to filter out heated air allowing only cool air to remain within his domain, significantly reducing the temperature.

In fact, it was precisely this principle that was used in modern cooling units to prevent equipment, electronics, and machinery from burning or melting. Thus, its cooling power could not be understated.

Yet, that was just one of many cooling elements that Rui had in mind.

"If high pressure yields high temperatures, then low pressures will yield low temperatures."

Gay-Lussac's Law worked both ways. Rui could drastically cool the environment by applying the inverse of Heavenly Convergence to direct pressure away from the domain, allowing it to cool significantly.

It was definitely functional as the second element of the Niflheim domain.

"Additionally, I get rid of heat by using the enthalpy of vaporization as a heat sink."

This was the same way an AC functioned. Air conditioners functioned by having liquids absorb heat from the environment to convert the liquid into gas, lowering the temperature of the environment.

What would happen if said AC was a billion times more powerful? What would happen if an AC became as powerful as a Martial Senior who could level a mountain at his or her peak?

That was what Rui aimed to be.

"I can temporarily convert gas into liquid within my lungs using pressure and then have the gas rapidly absorb heat as it turns into a gas

"Convection, pressure-cooling, and vaporization cooling."

These were the three elements of the Niflheim Domain that he had come up with.

They were powerful enough on their own, but Rui was not satisfied.

The Muspelheim domain had a fourth element that absorbed the enemy's energy and used it to heat the Muspelheim domain.

Unless Rui found a way to add the same energy-absorption element to the Niflheim domain, it would never be as strong as the Muspelheim domain. That was deeply dissatisfying to Rui.

He wanted the Niflheim domain to be as glorious and powerful as the Muspelhein domain was. He wanted both domains to be equally powerful such that if they were used simultaneously by two Rui's, the environmental temperature would remain unchanged because both domains would perfectly cancel out each other.

He refused to make any progress until he added a similarly powerful fourth element to the Niflheim domain.

Thankfully, his powerful mind delivered after it processed all the options at hand.

"Thermoacoustic cooling." Rui grinned as he found the answer.

This was a novel and cutting-edge form of cooling back on Earth in the twenty-first century that applied sound to absorb heat.

Sound waves were comprised of low-pressure and high- pressure zones. Thermoacoustic conditioning functioned by timing and spacing sound such that, in the low-pressure zones of a sound wave, the gas expanded and absorbed heat, and in the high-pressure zone, the gas contracted and expelled heat.

Thus, sound could transfer heat in a particular direction away from an area as long as the right frequencies were perfectly applied.

"I can absorb my opponent's energy using Flux Earther and use the sound it creates in the land to cool the Niflheim domain via thermoacoustic cooling."

This way, he could absorb his opponent's power to cool the environment down even further than the three elements of cooling that he had already created.

This way, the Niflheim technique could create an environment that was absurdly cold.

With this, it would be able to match its counterpart in the Muspelheim domain.

"Brilliant, with this, the theoretical framework of the Niflheim domain is complete. On top of that, I can significantly borrow from the training of the Muspelheim domain as well, further reducing the training time of the entire project.

"Thermoacoustic cooling is definitely going to be the hardest to train out of all four cooling elements of the Niflheim domain," Rui realized.

It was drastically different from anything he had done before; thus, it would definitely require the most focus out of all the training elements of Project Niflheim.

"Additionally, I can't forget that the body conditioning training needs to be applied side by side with these two domains in such a manner that progressive overload is never once broken. Otherwise, it could kill my gains."

The epithelial system, the entirety of the body's outer flesh, was replaced every twenty-seven days. He needed to ensure that the conditioning training adhered to that cycle to maximize the effects of the training, such that each cycle of skin was more resistant to cold and heat than the previous one.

Over two years, that was more than enough time to gain an immense amount of resistance to heat and cold. It was the same reason that workers who worked in furnaces had essentially become immune to the heat. Their epithelial tissue had been conditioned and had adaptively evolved to handle the heat over long timespan.

The Martial Body was even more extreme, with an even higher ability to condition and adaptively evolve to environments and forces. Thus, no matter how powerful these domains became, Rui was certain that he would be able to handle them without any issues, no matter what, as long as his training went right.

"Alright, time to begin."

He immediately commenced his training after fleshing out the training regimes and all the details in his head, dedicating exactly equal amounts of time to each domain. In hindsight, he was glad that he focused on only two domains rather than three.

"I should focus more on quality than quantity the stronger I get," he murmured.

The more techniques he had, the less quantity mattered. It was better to have a single grade-ten technique than three grade-eight techniques.

-