Magic Qi Refining Technique (Seeking Readership, Theories Too Long to Explain Will Be in Author's Notes)

The foundation of the Breathing Technique is to inhale and refine the magical factors in the air, transforming them into a special gaseous magical energy that flows through the meridians, then using specific techniques to concentrate it on the blade or throughout the body, forming elements.

According to Sakonji Urokodaki, the so-called schools of Breathing Technique mainly differ in the latter aspect; the former only varies in inhalation frequency and volume, with the technique itself being the same set.

Understanding these two points, Dan Lei immediately conducted experiments based on the magus theory of the Great Source and Od.

First, for convenience, Dan Lei directly named that special gaseous magical energy "True Qi," since its nature was roughly similar.

Then, Dan Lei began to court death, preparing to create his own Magic Qi Refining Technique.

For Dan Lei, using Magic Circuits in the Luofu to absorb the surrounding unclaimed power of the Path of the Hunt, causing his Magic Circuits to be damaged from time to time, had become a common occurrence.

After all, with the healing power of the Abundance Destiny in hand, as long as nutrition was sufficient and he didn't burn out all his Magic Circuits, a few months of recovery would do.

Of course, this repeated torment of the Magic Circuits, combined with the dragon bloodline of the Chizuru Clan, had indeed made Dan Lei's Magic Circuits much tougher than those of an average magus.

So Dan Lei began using his Magic Circuits to absorb Mana, directly infiltrating the True Qi's meridians from the inside, attempting to achieve [Total Concentration Constant] through this method.

Then, Dan Lei succeeded in rupturing all his meridians.

It wasn't difficult for the Mana from the Magic Circuits to seep into the True Qi's meridians, but this Mana was anything but gentle—after all, in the anime, when Mana passes through Magic Circuits in large quantities, it tends to come with lightning effects.

Thus, Dan Lei's barely trained meridians instantly ruptured, even affecting his Magic Circuits, and he directly spat out a mouthful of blood.

Fortunately, the Power of Abundance healed him, and his life was saved.

Later, Kojiro Sasaki brought two Wild Mountain Ginsengs for his death-seeking Master, and Dan Lei used the medicinal power to fully repair his meridians.

After one brush with death, Dan Lei dared not be so aggressive again, directly letting Mana from his Magic Circuits enter his meridians.

So he changed his target, using the Mana from his Magic Circuits to enter his lungs, attempting to convert Mana by the same method used to convert magical particles in the air, thereby enhancing True Qi.

As a result, this experiment was half successful.

The Mana from the Magic Circuits could indeed be converted into True Qi in the lungs, but the efficiency was abysmal.

Because the Mana stored in the Magic Circuits had already been refined by Dan Lei, its quality was far higher than the magical particles in the air.

And Dan Lei was only a beginner in the Breathing Technique—it was like making a baby's stomach, still only able to digest milk, absorb meat; indigestion was the least of the problems.

However, with the power of the Abundance Destiny, ordinary injuries were harmless to Dan Lei.

Moreover, Dan Lei accidentally stumbled upon a Breath Holding Technique during this experiment: when converting Mana from his Magic Circuits into True Qi, it produced oxygen, and as long as the stripped carbon didn't exceed Dan Lei's tolerance limit, he could hold his breath for extended periods.

Of course, this ability was rather useless to Dan Lei. The Chizuru Clan's Cloud Chant Technique already had a secret method for breathing underwater, so without the High Elder parting the sea, even Chizuru who didn't know the Cloud Chant Technique could still enter the Scale Abyss Realm to transform and be reborn, as long as someone led them.

As for space, Pathstriders, in theory, as long as they were strong enough, could obtain all the energy their bodies needed from the Imaginary Energy of their Path.

Those Pathstriders who could physically go into space would wrap themselves in Path energy, isolating all cosmic radiation and internal-external pressure differences, and then all the energy the human body needed would be supplied by the Path energy, allowing them to fight in space without protection.

Of course, that had nothing to do with Dan Lei. To repeat, Dan Lei had never seriously studied the Abundance Destiny. Although he kept improving by constantly tormenting himself, he was still far from being able to go into space with his bare body.

So, after half a year of torment, Dan Lei concluded that haste makes waste. He first needed to solve the problem of the lungs' conversion efficiency before he could continue researching the Magic Qi Refining Technique.

How to enhance the lungs' conversion efficiency? Naturally, by diligently practicing the Breathing Technique.

Fortunately, Dan Lei hadn't wasted the past six months torturing himself. His lungs had been so thoroughly ravaged that they were now practically iron lungs. Once he started training in the Breathing Technique, his progress was once again rapid.

At this time, Tanjiro was still in the period of training his physical agility and practicing sword swings.

Of course, Dan Lei didn't need to follow the agility training, but he couldn't escape the sword swings.

Moreover, Dan Lei and Tanjiro's sword swing practice was personally supervised by Kojiro Sasaki. Aside from fishing and catching demons, his job was to watch the two swing their swords. If anything was off, he would immediately hit them with a branch and correct their posture.

Yes, Kojiro Sasaki's job also included catching demons. While Dan Lei was tormenting himself with the Magic Qi Refining Technique and the Breathing Technique, he hadn't forgotten to continue researching demons and Nezuko's Ley Line Energy Absorption ability.

At night, while Tanjiro was studying cultural lessons and writing in his diary, Dan Lei would go torment the demons Kojiro Sasaki had captured.

Given Kojiro Sasaki's strength, the Upper Ranks were unknown, but the Lower Ranks and other demons were absolutely one-shot kills.

It was known that a demon's abilities and activity level were tied to Mana. So Dan Lei only needed to create a box that could seal Mana. Kojiro Sasaki would cut off the demon's limbs, stuff it into the box, and bring it back in a sealed state.

Lower Rank demons weren't so easy to encounter, and Dan Lei didn't want to wipe out the ones whose locations he knew just yet. So the demon intel was actually provided by Sakonji Urokodaki, and whether they had a Blood Demon Art was purely a matter of luck.

But that didn't affect Dan Lei's research. After all, there was no need to treat demons humanely, so he could do whatever he wanted.

Sakonji Urokodaki agreed with this, and later even became Dan Lei's assistant in demon research.

Thus, it didn't take long for Dan Lei to confirm, through over a dozen demons with Blood Demon Art potential, that the Blood Demon Art was indeed a demon's awakened ability, innate and impossible to imitate.

Because all demons with Blood Demon Art had unique and independent internal differences, and would even grow corresponding organs for their abilities. Dan Lei had no desire to turn himself into an alien. In the end, he only recorded the Mana operation trajectories and structures of these organs.

However, Dan Lei had made some progress in researching how demons absorbed ley line energy. Through extensive controlled experiments, he was able to reconstruct the energy absorption model from the fluctuations of demons absorbing ley lines.

Plus, by this time, Nezuko had fallen into a deep sleep, beginning to absorb large amounts of ley line energy to complete her evolution. With real-time data, Dan Lei naturally refined the model and reconstructed the demon's Ley Line Energy Absorption Matrix.

Next, he just needed to create a magical item based on this matrix to wear. This item wouldn't absorb a large amount of ley line energy, but it would be persistent. Wearing it constantly could at least shorten the Holy Grail's charging time by three to five years.

The best materials for this magical item would be from demons themselves, but Dan Lei found those man-eating demons disgusting, so he directly plucked some of Nezuko's hair while she was asleep to make it.

Of course, Dan Lei asked for Nezuko's opinion before cutting her hair, and she didn't object.

Tanjiro did object, but his objection was overruled. In the end, Dan Lei used Nezuko's hair as a medium, combined with a Mana absorption array, to make a waist accessory. This way, it could continuously absorb energy from the ley lines—at least in this world.

As the life force of the planet, the Great Source (Mana) manifests in forms including: ley line energy (such as the spiritual veins of Fuyuki City), magical particles in the atmosphere, and life fluctuations generated by natural cycles. In a typical case, during the Fifth Holy Grail War, Rin Tohsaka could replenish Mana through the ley lines at a rate of approximately 2,000 units per hour.

This energy is similar to the concept of "Heaven and Earth Spiritual Qi" in cultivation systems, requiring conversion through a specific Magic Foundation for use.

Od, as the Life Energy within living organisms, possesses the following characteristics:

An ordinary human naturally produces approximately 10-50 units per day.

A magus can store 300-3000 units through their Magic Circuits (depending on circuit quality). Excessive consumption can lead to organ failure (as in the case of Kariya Matou).

Its operational mechanism is highly similar to the "internal energy" in martial arts novels, both requiring transmission through specific meridians (Magic Circuits).

However, in the Nasuverse, aside from natural biological growth or finding ways to undergo a life leap (such as fusing with Phantom Beast or Demonic Beast bloodlines, or becoming a high-ranking Dead Apostle), Od can hardly be increased through training (physical exercise yields negligible improvement). One can only continuously optimize usage efficiency (a typical example being Aozaki Touko).