Sasuke understood the book's arguments. After all, Fire Release ninjutsu essentially involved injecting "attribute-less" chakra into Fire Release chakra, thereby releasing it.
Practicing and mastering numerous Fire Release techniques daily naturally enhanced and refined one's Nature Transformation abilities.
Some advanced Fire Release techniques, beyond Nature Transformation, also required Shape Transformation.
Techniques like the Great Dragon Fire Technique, Dragon Flame Song Technique, and Phoenix Flame Dance Technique transformed simple fireballs into lifelike fiery dragons and phoenixes through compression and shaping, concentrating or expanding the technique's power and attack range.
'Is the method described in the book the only way?'
Directly practicing Nature Transformation like Naruto would be too slow given Sasuke's current circumstances.
Following the book's method wouldn't be ideal either.
At his current stage, Sasuke could only manage to practice two or three Fire Release techniques per day.
To maximize his progress, he reserved most of his chakra for his Shadow Clones to focus on learning.
'Hmm...'
The defining characteristic of Fire Release is heat—or more precisely, extreme heat.
Since the knowledge of this world couldn't solve Sasuke's current predicament, he turned to the knowledge he had acquired in his previous life.
From a physics perspective, temperature is a measure of the intensity of the thermal motion of an object's molecules.
The faster the molecules move, the higher the temperature and the hotter the object; conversely, the slower the molecules move, the lower the temperature and the colder the object.
As the saying goes, friction generates heat!
Realizing this, Sasuke's face lit up with sudden understanding, as if he had grasped a crucial insight.
"If my theory holds true, then..."
Acting on his realization, Sasuke once again gathered a ball of chakra in his palm.
At this point, he didn't fully understand the true nature of chakra, nor did he know if it contained molecules, atoms, or anything similar.
But that didn't stop him from mimicking the principles of molecular thermal motion.
Though still a ball of chakra in his hand, beneath its surface, countless microscopic chakra particles were being remotely controlled to collide and move in a slow, continuous motion, mimicking the frictional movement between molecules.
As soon as he held his hand over the kettle, visible steam began to rise within seconds, and the water inside resumed boiling.
"Hahahahaha! Just as I thought!"
"The ancestors were right all along—science is power!"
Seeing this, Sasuke couldn't help but feel a surge of elation.
But his elation lasted only a few breaths before he quickly regained his composure and continued pondering.
First, at standard atmospheric pressure, water boils at 100 degrees Celsius.
This temperature is barely adequate for dealing with ordinary people, and utterly insufficient against ninjas. Trying to defeat enemies solely with Fire Release chakra from his hands would be practically impossible.
In the future, he could compensate for this by increasing the velocity of the minute chakra particles within his Fire Release chakra, potentially achieving a level comparable to the Wind Release: Rasenshuriken.
However, this would require further training in chakra control.
Second, this could be an advantage. By mimicking molecular thermal motion, Sasuke could incorporate the principles of intermolecular movement into his Fire Release chakra techniques, allowing him to unleash Fire Release ninjutsu like the Great Fireball Technique from his mouth with even higher temperatures and greater velocity!
However, he must be cautious. If the chakra within his mouth moved too rapidly, it could become unstable and burn his oral cavity.
Solving one problem only led to two more arising, but Sasuke didn't mind in the slightest.
The more intelligent a person is, the more problems they uncover, the more keenly aware they become of their own shortcomings, and the more humble they grow.
Only a frog at the bottom of a well would mistake the well's opening for the entire sky.
Sasuke quietly closed his eyes. As long as he could identify the problems and confirm he was on the right path, nothing else mattered.
Following his usual routine, he summarized the day's gains on paper, reviewed them in his mind, and then destroyed the notes.
Night had deepened. Sasuke had finished his day's training and entered his room, but he didn't immediately rest.
Instead, he lay prone on a cushion on the tatami mat, elbows bent, palms pressed against the floor at his sides, legs extended straight, the backs of his feet pressed against the floor.
He inhaled, straightened his elbows, and lifted his body off the ground, supported by his palms and the backs of his feet. Exhaling, he tilted his head back, gazing up at the ceiling.
With each forward bend, he exhaled, and with each contraction, he inhaled deeply, creating a peculiar, rhythmic movement.
Yoga!
The exercises Sasuke was performing were, of course, yoga postures from his previous life.
In his previous life, Sasuke had been a fitness enthusiast. Like most men, he'd focused on weightlifting, while his girlfriend practiced yoga.
Though he'd never practiced yoga himself in his past life, years of cohabitation and osmosis had made him thoroughly familiar with the practice.
He knew the key points and proper form for each pose by heart.
Two months ago, after deciding on his cultivation plan, Sasuke began studying yoga seriously.
Every night before bed, he dedicated an hour to yoga practice.
Yoga is an exercise that trains physical flexibility while promoting blood circulation and detoxifying the body.
During practice, it provides a massage-like effect, making it an excellent relaxation method for someone like Sasuke, who subjected himself to near-demonic training regimes daily.
Beyond its physical benefits, yoga also soothes the mind and spirit, fostering focus, concentration, and meditative stillness.
The "meditation practice" Sasuke had included in his plan to increase his spiritual energy specifically referred to yoga and its associated meditation techniques.
In ancient times, Yoga was one of the Six Major Philosophical Schools.
Its practice was divided into seven stages, corresponding to the seven chakras: Root Chakra, Sacral Chakra, Solar Plexus Chakra, Heart Chakra, Throat Chakra, Third Eye Chakra, and Crown Chakra.
Reaching the highest state of practice led to the Brahman-Atman Union, a state of complete union between the individual self and the ultimate reality.
Legend has it that Buddha Shakyamuni, before his enlightenment, was a master of Yoga's ascetic practices.
Later, Buddhism's meditation techniques, known as Dhyana, incorporated many elements of Yoga's meditative practices.
The Yoga Sasuke practiced was naturally not the ancient religious form, but rather the modern fitness and mindfulness exercises commonly taught in studios on any street.
The concept of Chakra in the Naruto world originates from Yoga's energy centers, referring to the vital energy nodes distributed throughout the human body, particularly those aligned along the central axis from the tailbone to the crown of the head—the Three Channels and Seven Chakras!
Sasuke remained uncertain about any specific connection between Yoga from his past life and Chakra in this world.
However, after two months of practice, he could clearly sense his mental clarity improving, and his speed in refining and circulating Chakra had also increased.
A win-win: enhancing his strength while promoting physical and mental well-being.
Sasuke persevered, refusing to give up.