At Mount Taoyuan, the waterfall roared.
Tanjirou and Agatsuma Zenitsu were struggling in the turbulent currents beneath the waterfall, practicing the Thunder Breathing sword forms.
The water was icy cold and its impact was immense.
Every swing of their swords required them to mobilize their entire body's strength and Full Focus Breathing.
Kuwajima Jigorō stood on the bank with his arms crossed, his expression stern, but deep in his eyes was a hint of satisfaction at the rapid progress of the two boys.
Especially Tanjirou, whose solid foundation and the integration of Qi Refining Technique allowed him to progress at an astonishing speed.
Even Zenitsu, who was always crying, displayed an eerily fast First Form when forced to be serious.
Suddenly, Kuwajima Jigorō raised an eyebrow.
A nearly imperceptible, amused smile appeared at the corner of the old man's mouth, as if he was watching a good show.
"Hmm, it seems the 'extra' training has arrived."
Before he finished speaking, a blue-white lightning bolt, as if tearing through space, sped from the mountain forest at an uncatchable speed, instantly landing by the waterfall pool and revealing Cheng Mo's figure.
The subtle electric arcs around him slowly faded, his expression as calm as ever.
"Waaah! Not, not again!"
Zenitsu was the first to notice, so scared he almost dropped his sword.
He slipped into the water with a splash, choked on several mouthfuls before scrambling out miserably, hiding behind Tanjirou, trembling.
"Tanjirou, the demonic Senior Brother is here again! He's going to strike us with lightning, it hurts so much!"
Tanjirou also tensed up, unconsciously standing a little straighter.
A happy expression appeared on the boy's face: "Teacher!"
Kuwajima Jigorō chuckled twice: "Boys, enjoy it! This is a privilege others can only dream of!"
He had witnessed Cheng Mo's incredible training methods; though cruel, their effectiveness was outstanding.
Cheng Mo offered no pleasantries, his gaze directly fixed on Tanjirou.
"Come here."
Tanjirou immediately gritted his teeth and, fighting against the waterfall's torrent, painstakingly walked to the bank.
Cheng Mo extended a finger, and extremely subtle, yet scalp-prickling, azure electric sparks danced at its tip.
The next moment, with a speed Tanjirou couldn't possibly react to, his finger tapped several key muscle groups and meridian points on his body.
"Ugh—"
Tanjirou instantly let out an uncontrollable, pained groan, his whole body trembling violently.
Having followed his teacher for so long, he felt he should have adapted to his teacher's electric currents by now... but... he didn't know why, it felt like his teacher's electrical stimulation had changed recently.
As if it targeted deeper levels of the body!
It was like countless red-hot needles simultaneously piercing the deepest parts of his body, an indescribable pain—sore, numb, and agonizing—instantly swept through him, every muscle screaming and twitching!
But he clenched his jaw tightly, veins bulging on his forehead, sweat pouring out like streams, mixing with the waterfall's spray.
He could feel that beneath this extreme pain, some kind of restraint deep within his body seemed to be forcibly broken open.
The Qi Refining Technique's operation speed involuntarily accelerated, and his control over his breathing was also forced to improve under this extreme stimulation.
"Hold on, Tanjirou!"
Kuwajima Jigorō encouraged him loudly from the side.
Zenitsu, hiding behind him, turned pale and his eyes welled up with tears:
"No... this looks even scarier than being struck by lightning... I'm going to die, I'm definitely going to die..."
Soon, Cheng Mo ended the electrical stimulation.
Tanjirou was almost completely exhausted, kneeling on one knee, gasping for air, his body still trembling slightly uncontrollably, but his eyes were exceptionally bright.
He felt his body had indeed become... lighter, and his senses sharper.
Cheng Mo's gaze shifted to Zenitsu, who was trying to hide himself behind the waterfall.
"You too."
"No—I'm sorry, I'll practice my sword diligently, I don't want to be shocked! Grandpa, help! Tanjirou, help!"
Zenitsu let out a desperate cry, but under Cheng Mo's unwavering gaze and Kuwajima Jigorō's "benevolent" stare, he was eventually dragged over by Tanjirou and received the same "treatment."
He cried earth-shatteringly, as if undergoing immense torture.
However, it wasn't over yet.
Cheng Mo looked at the two, who had barely recovered, and spoke again: "Concentrate, maintain your Breathing Technique."
He stood in place, unmoving.
But an invisible, mountain-heavy pressure suddenly descended!
This was not killing intent, but a kind of spiritual pressure derived from a stronger, more refined soul essence.
Like an undercurrent in the deep sea, it silently crushed down, directly affecting their minds and consciousness.
Tanjirou and Zenitsu both felt a sudden "buzz" in their heads, and their breathing abruptly hitched.
Their hearts felt as if squeezed by an invisible hand; a sense of inexplicable fear and insignificance arose, as if standing on the edge of a bottomless abyss, their thoughts becoming sluggish.
"Brea...the..."
Cheng Mo's cold voice struck their almost stagnant consciousness like a hammer.
Tanjirou bit the tip of his tongue sharply, the intense pain clearing his mind slightly.
He desperately recalled the rhythm of the Qi Refining Technique and Full Focus Breathing, resisting the pervasive mental pressure, trying to stabilize his trembling body and maintain the operation of his Breathing Technique.
Zenitsu was even more terrified, tears streaming down his face, his legs too weak to stand, but the pressure prevented him from even falling, forcing him to desperately and intermittently maintain his breathing.
His mind was blank, leaving only instinctive fear and the struggle to maintain his breathing.
This process was not long, only about ten seconds.
The pressure suddenly vanished.
The two gasped for air, as if rescued from drowning, their backs completely drenched in cold sweat.
"Waaah... I was so, so scared..."
Zenitsu slumped to the ground, still sobbing.
"I felt like my soul was going to fly away..."
But strangely, as the fear slowly receded, he found that his attention, which had been highly concentrated due to extreme terror, was now exceptionally clear.
The sound of the surrounding waterfall and the rustling of leaves became remarkably distinct, and even the Thunder Breathing · First Form, which had always been difficult to control precisely, seemed a little clearer in his mind?
Tanjirou had a similar feeling.
Although the immense pressure was terrifying, it was like a hammer that shattered the slight distractions and fatigue he had accumulated from days of arduous training, making his mind more refined and focused instead.
Kuwajima Jigorō looked at the two boys' states, stroking his chin, a hint of surprise and understanding flashing in his eyes.
He couldn't teach this method of tempering the will.
Cheng Mo, that little monster, his methods were truly becoming more unfathomable.
And Cheng Mo, observing their reactions, silently assessed the effectiveness of the soul pressure training.
After confirming they were temporarily fine, his figure once again transformed into lightning and instantly vanished from Mount Taoyuan.
Leaving behind only two boys with lingering fears and an old man who enjoyed watching the show.
He had to return to the laboratory as soon as possible; there, the research on soul and blood had just achieved a breakthrough direction.