This isn't a chapter per se. Think of it as some sort of side-story (a side-conversation if you will). Over the course of this story, there will be many such conversations between Sesha and Rudra where the master will be teaching (you) Sesha about the yoga itself. You can skip this conversation but if you do so, you won't have a complete understanding about why Sesha knows the things that he knows and does the things that he does.
Finally, I think that this particular conversation belongs somewhere before Chapter 12. I will move it there as soon as I figure out how.
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Time: Few months after Nagini left the Dark forest.
Rudra, who was sitting before his disciple in a lotus position, said to him,
"Sesha, today I will explain to you about Swadhisthana."
"But master, haven't you already explained about Swadhisthana to me before?" a puzzled Sesha asked.
"No. What I have previously taught you about the water chakra can only said to be elementary. Besides, now that you have stepped into the water realm yourself, it is high time you learned to use the Swadhisthana."
After his master had spoken, Sesha suppressed any other questions he had and instead began to intently listen to his master, not wanting to ignore even a single word.
Rudra reiterated the elementary knowledge about the Swadhisthana chakra; like its six petaled structure, the crescent shape inscribed within it and its color. Apart from that, he also repeated about its attributes, its bodily location and the meridians that entered and exited it.
After explaining the basic things once again, Rudra concluded,
"But you know these things already. What you do not yet know, are the benefits of Swadhisthana. Young Sesha, many disciples tend to belittle Swadhisthana because it does not have any offensive arts associated with it. Of course, they are utterly mistaken. Despite of not having any attacking arts, the water chakra is extremely important, if not the most important, for a disciple. Do you know why?"
Rudra asked with his eyes raised. Sesha replied in an unsure tone.
"Is it because Swadhisthana is extremely passive?"
Seeing his disciple answer such a profound (vague) question with an equally profound (vague) answer, his master couldn't help but give a chuckle.
"Haha, you really are an observant pupil Sesha. It is indeed what you say. The other six chakras of the body can not be used rashly or they will have severe repercussions. Manipura, the fire, being the most dangerous of them all. But Swadhisthana in contrast, is an extremely forgiving chakra. Even if you are a bit excessive in using this chakra, you will not suffer any serious bodily harm. In this aspect, it takes after the water element, cool and forgiving.
"With this property of the Swadhisthana, it is the most suitable chakra to practice the control of essence."
"Essence, master?" Sesha asked.
"Oh right, you do not know about essence of chakra right? Think of it this way, essence is the purest form of prana that a chakra holds. You know that Muladhara holds the prana of earthen nature right? Then essence of Muladhara would be the embodiment of earth itself. Each chakra holds such essence of its own. It is this essence, in fact, which inspire the prana's nature. For example, if prana that you intake from the universe, enters the Muladhara, it acquires earthen nature due to being in contact of the essence of Muladhara. Similarly, if it enters Swadhisthana, it acquires nature of water due to it being in contact with the essence of Swadhisthana.
"Normally, a yogi does not touch these essences. After all, if the essence of a chakra depletes, the chakra becomes useless as it would not then be able convert the pure prana into its equivalent attribute resulting in the waste of the yogi's entire cultivation. But if and when a yogi uses it, the effects of using the essence itself is at least a thousand times more potent than when using the elemental prana from the chakra.
"This is also the reason why the essence is dangerous. If not controlled properly, it would rage over the yogi's entire body devouring it in process. For instance, if you were to misuse the essence of Muladhara, your entire body will harden to the point that even the softest touch would shatter you. This is the reason why I did not teach you about the essences when you were still in the first realm lest you became overly curious. But now is different.
"Since you have already opened your Swadhisthana, I can begin to show you the usages of its essence. It is not entirely void of dangers but compared to other chakras, Swadhisthana is so forgiving that these dangers are extremely minute."
The narrative has been illicitly obtained; should you discover it on Amazon, report the violation.
Rudra looked at Sesha who had a face full of understanding. This made him happy because the things that he had said in such a short span of time were indeed a little difficult. Even if he knew that his disciple had an outstanding memory and perception, an effect of his innately open third eye, he was a little afraid that his teachings would exceed his disciple's understanding. Clearly, it was not the case. Sesha had listened to and absorbed every single word that he had said. With a satisfied smile befitting a proud master of a perceptive disciple, he proceeded to the next part of his teachings.
"Since these essences are so powerful, how many yogis among a thousand do you think have used essences from a chakra at least once?" Rudra asked his disciple.
"How many master?"
"None." Rudra replied simply and added, "Even among a hundred thousand yogis, only a single one has used his essence at least once in his entire life."
"Master, are the dangers from essence so much that not even a single one among a thousand would dare tap into it?" Sesha was perplexed.
Even if the dangers of using these essences were quite a lot, Sesha had expected a larger number from his master. Besides, didn't his master say that using essence from Swadhisthana was almost harmless?
"My disciple, it is not that they would not dare use the essences, it is that they can not use it. Do you perhaps think that using such a potent power is so easy that anyone could do it at his will?
"The essence itself is the embodiment of nature and wielding the power of nature can only be described as divine. Naturally, not every one is capable to wield it!"
"Umm.. master, can I use it?" Sesha inquired.
"Haha, of course you can!! Do you not know whose disciple you are!! In but a span of ten years, you will be an adept at using your essence at will!!" Rudra laughed at his innocent disciple's question as he sensed his disciple's fear of disappointing his master.
"But master.. Won't it harm my cultivation if I were to use it so freely!?"
"Indeed it will! But tell me this, young Sesha. Would you use it so frivolously?"
"Of course not master !!" Sesha said unhesitatingly.
At his disciple's reply, the master's face broke into one of smile.
"See, since you know the dangers of using the essence yourself, I am sure that you'll use it sparingly. Besides, you happen to have a larger amount of essence in each of your activated chakra save for the Ajna, so there should be no danger to your cultivation whatsoever."
Sesha's face showed that him possessing a larger amount of essence was a news to him. But before he could ask his master anything about that, his master had already continued.
"It took you not more than one and a half year to conquer your Muladhara and within next five months, you opened your Swadhisthana. It has been but a couple of months since then but your progress with Swadhisthana could only be said as astonishing. I am confident that within another two years, you would completely conquer the Swadhisthana. However, I do not want you to continue like this.
"From now onwards, you are to cultivate your control over the essence of Swadhisthana. After you have perfected your control of Swadhisthana's essence, you will then cultivate the essence of Muladhara. Even with your talents, I suspect it would take you five years to completely control the essence of Swadhisthana (AN: it took him two years) and then ten years to control the essence of Muladhara (AN: It took him three years).
"Only after you have mastered the essences, will I allow you to cultivate further. Do you understand young Sesha? Even after you have left this forest, you must always cultivate the essences as early as possible. And beware my disciple, there are some forbidden medicines that allow one to use the power of essences for a short while but you must, at all cost, avoid them! These medicines provide a lure of great power but if you use them, they would undoubtedly cripple you, if not kill you! You must not become impatient while walking the path of yogic cultivation!"
Rudra sternly commanded him! This disciple of his was extremely important to him. As such, he did not want Sesha to make a foolish mistake and end up crippled or dead.
"Since I have said everything that I needed to say, I will now show you the method of essence cultivation..."