The foundation of the Breathing Technique was to refine magic particles in the air by inhaling, turn them into a special gaseous form of magic that flowed through the meridians, and then use special techniques to gather it on the blade or around the body, forming an element.
According to Sakonji Urokodaki, the different schools of the Breathing Technique mainly differed in the latter part. The former differed only in the frequency and volume of inhalation; the techniques themselves were all the same.
Having understood these two points, Dan Lei immediately began experimenting with them based on the theories of the Great Source and Od used by mages.
First, for convenience, Dan Lei directly named that special gaseous magic True Qi. Its properties were pretty similar, anyway.
Then Dan Lei started doing something reckless: he prepared to create his own Magic Qi Refining Technique.
For Dan Lei, damaging his Magic Circuits now and then by using them to absorb unclaimed power from the Path of the Hunt around him on the Luofu had become commonplace.
With the healing power of Abundance Destiny at hand, all he needed was enough nourishment. As long as he didn't burn out all his Magic Circuits, a few months of recuperation would fix them.
Of course, repeatedly tormenting his Magic Circuits like this, combined with his Chizuru Clan dragon blood, had indeed made them much tougher than those of an ordinary mage.
So Dan Lei began absorbing magic with his Magic Circuits and letting it seep straight into the meridians that carried True Qi, hoping to achieve [Total Concentration Constant] this way.
Then Dan Lei succeeded in damaging all the meridians in his body.
It wasn't difficult to let the magic in his Magic Circuits seep into the True Qi meridians, but that magic was anything but gentle. After all, the anime showed magic passing through Magic Circuits with flashes of lightning whenever the amount was too great.
As a result, Dan Lei's barely trained meridians were damaged in an instant, even affecting his Magic Circuits. He spat out a mouthful of blood.
Fortunately, the Power of Abundance healed him, and he survived.
Afterward, Kojiro Sasaki brought two Wild Mountain Ginseng roots for his reckless Master. Dan Lei needed their medicinal power to completely repair his meridians.
After that first reckless attempt, Dan Lei didn't dare let the magic in his Magic Circuits flow directly into his meridians so aggressively again.
Instead, he tried a different approach. He sent the magic from his Magic Circuits into his lungs and other organs, attempting to convert it into True Qi by using the method that transformed magic particles in the air.
As it turned out, the experiment was only half successful.
The magic from his Magic Circuits could indeed be converted into True Qi in his lungs and other organs, but the efficiency was downright terrible.
That was because the magic stored in his Magic Circuits had already been refined by Dan Lei, making its quality far higher than that of the magic particles in the air.
Meanwhile, Dan Lei was only a beginner at the Breathing Technique. It was like asking a child who could only drink milk to digest meat. Indigestion would be the least of his worries.
But with the power of Abundance Destiny, ordinary injuries were nothing to Dan Lei.
What's more, by a stroke of luck, the experiment led Dan Lei to learn a Breath Holding Technique. When the magic in his Magic Circuits was converted into True Qi, it produced oxygen. As long as the amount of carbon he separated out didn't exceed what Dan Lei could tolerate, he could hold his breath for a long time.
Of course, this ability was pretty useless to Dan Lei. The Chizuru Clan's Cloud Chant Technique already included a secret method for breathing underwater. So even without a High Elder opening the sea, a Chizuru Clan member who didn't know the Cloud Chant Technique could still enter the Scale Abyss Realm and transform into an egg, as long as someone led the way.
As for outer space, Pathstriders could theoretically obtain all the energy their bodies needed from the Imaginary Energy of their Paths, as long as they were strong enough.
Those Pathstriders who could travel into space with their bodies simply wrapped themselves in Path energy, blocking out all cosmic rays and pressure differences between the inside and outside. Their bodies' energy needs were then entirely met by their Path energy, allowing them to fight in space without protection.
Of course, that had nothing to do with Dan Lei. As mentioned before, he hadn't properly studied Abundance Destiny. Although constantly putting himself through the wringer had helped him improve, he was still a long way from being able to go into space with his body alone.
So, after half a year of tinkering, Dan Lei reached one conclusion: haste made waste. He first needed to improve the efficiency with which his lungs and other organs converted magic before he could continue researching the Magic Qi Refining Technique.
How could he improve that conversion efficiency? Naturally, by diligently practicing the Breathing Technique.
Fortunately, Dan Lei hadn't spent the past six months abusing himself for nothing. His lungs and other organs had been battered until they were practically made of iron. Once he began practicing the Breathing Technique, his progress was once again rapid.
At this point, Tanjiro was still training his agility and practicing his sword swings.
Of course, Dan Lei didn't need to train his agility with him, but he couldn't get out of practicing his sword swings.
Moreover, Kojiro Sasaki personally supervised Tanjiro and Dan Lei's sword practice. These days, aside from fishing and hunting demons, he watched the two of them swing their swords. Whenever either of them did something wrong, he would strike them with a branch and correct their form.
That's right, Kojiro Sasaki's duties included hunting demons, too. While Dan Lei was tinkering with the Magic Qi Refining Technique and the Breathing Technique, he hadn't forgotten to continue researching demons and Nezuko's ability to absorb Ley Line energy.
At night, while Tanjiro studied his lessons and wrote in his diary, Dan Lei would experiment on the demons Kojiro Sasaki had brought back.
With Kojiro Sasaki's strength, it was hard to say how he'd fare against an Upper Rank, but he could certainly kill a Lower Rank or any other demon in an instant.
Since demons' abilities and activity levels were known to be linked to magic, all Dan Lei needed to do was make a box that could seal magic. Kojiro Sasaki could chop off a demon's limbs, stuff it in the box, and bring it back in a sealed state.
Lower Rank demons weren't easy to find, and Dan Lei didn't want to go after the few whose locations were known just yet. So the information about demons mostly came from Sakonji Urokodaki, and whether any of them had a Blood Demon Art was left to chance.
That didn't affect Dan Lei's research. There was no need to show demons any humanity, so he could do whatever he wanted to them.
Sakonji Urokodaki agreed with this approach, too. Later on, he even became Dan Lei's assistant in researching demons.
So it wasn't long before Dan Lei confirmed with more than a dozen demons who had an innate talent for Blood Demon Art that Blood Demon Arts really were awakened abilities unique to demons. They were inborn and couldn't be imitated.
Every demon with a Blood Demon Art had a unique and independent ability. Some even grew the corresponding organs for their powers. Dan Lei had no desire to turn himself into some kind of monster. In the end, those organs merely helped him record the magic's flow and structure.
Dan Lei had already made some progress in researching demons' ability to absorb Ley Line energy. After conducting a large number of comparative experiments, he was able to reconstruct an energy absorption model from the fluctuations produced when demons absorbed Ley Line energy.
By then, Nezuko had fallen into a deep sleep and begun absorbing large amounts of Ley Line energy to complete her evolution. With real-time data to work from, Dan Lei was naturally able to refine the model and reconstruct the demons' Ley Line Energy Absorption Matrix.
Next, all he needed to do was use the matrix to make a magic item that he could wear. The item wouldn't absorb much Ley Line energy, but it would do so steadily. Wearing it all the time could shorten the Holy Grail's charging time by at least three to five years.
Ideally, the materials for this magic item would all come from demons. But Dan Lei found those man-eating demons disgusting, so he simply snipped some hair from the sleeping Nezuko's head to make it.
Of course, Dan Lei asked Nezuko for permission before cutting her hair, and she didn't object.
Tanjiro did object, though, but his objection was overruled. In the end, Dan Lei used Nezuko's hair as a medium and combined it with a magic absorption array to make a waist accessory. That way, it could continuously absorb energy from the Ley Line—at least, in this world.
The Great Source (Mana), the life force of a planet, takes several forms: Ley Line energy (such as Fuyuki City's leylines) Magic particles in the atmosphere Life fluctuations produced by natural cycles (a typical example: during the Fifth Holy Grail War, Rin Tohsaka replenished her magic through the Ley Line, drawing about 2,000 units of Mana per hour). This energy is similar to the concept of "spiritual energy of heaven and earth" in cultivation systems, and must be converted through a specific Magecraft foundation before it can be used. Od, the life energy within living beings, has the following properties: Ordinary humans naturally produce about 10–50 units per day. Mages can store 300–3,000 units through their Magic Circuits, depending on their quality. Excessive consumption can lead to organ failure (as in Kariya Matou's case). Its operating principles are highly similar to the "inner power" of wuxia novels, with both requiring transmission through specific meridians (Magic Circuits). However, in the Nasuverse, Od can hardly be increased through training alone. Aside from natural growth or finding a way to undergo a life-form transition (such as fusing with the bloodline of a phantasmal or magical beast, or becoming a high-ranking Dead Apostle), physical training offers only a negligible improvement. The only option is to continually improve the efficiency with which it is used (a typical example: Aozaki Touko).
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