Over the next few days, Cheng Mo settled Tanjirou in Peach Mountain.
Kuwajima Jigorō's training was as rigorous as ever, almost cruel.
In the early morning, the roaring sound of the waterfall became the bugle call for training.
The old man made Tanjirou and Zenitsu stand side by side directly under the waterfall, enduring the violent impact of the icy torrent.
"Stand firm! Engage your core, don't break your breathing, maintain Total Concentration Breathing!"
Kuwajima Jigorō's voice cut through the booming sound of the water.
"Swing your sword! Five thousand times! Not one less, if your form deforms, start counting from the beginning!"
Tanjirou gritted his teeth, his feet firmly gripping the slippery rocks, as the huge current slammed down on his head and shoulders, bringing dull aches and bone-chilling cold.
His entire body was tense, and the sweat that emerged was immediately washed away by the torrent.
Each breath became incredibly difficult, but he painstakingly drew upon the solid foundation laid by his Qi Refining Technique, striving to adjust his breathing rhythm so that his lungs could still effectively take in oxygen despite the powerful water pressure and cold stimulation.
The wooden sword he swung repeatedly cut through the water, his movements slightly sluggish due to the harsh environment.
But his core stability and method of exerting force remained steadfast, his gaze as firm as a rock.
Next to him, Zenitsu's screams were even louder than the waterfall: "Ah ah ah—I'm going to die, I'm going to die! I can't breathe, my nose and ears are full of water, my bones are going to break, Grandpa, people really will die!"
He cried with snot and tears streaming down his face, looking like he would be washed away any second.
But strangely, despite his wailing, his body remained remarkably stable in the torrent.
His feet seemed to have taken root.
And the wooden sword Zenitsu swung, each angle and force was terrifyingly precise, cutting through the water cleanly and smoothly, even more fluid than Tanjirou's.
The more tragically he cried out, the more exquisitely his breathing rhythm unconsciously adjusted.
It perfectly embodied the essence of Thunder Breathing's pursuit of extreme speed and explosive power.
In the difficult pauses between his sword swings, Tanjirou noticed Zenitsu's extremely contradictory performance and became even more convinced—
This seemingly timid and crybaby Zenitsu was definitely not as simple as he appeared on the surface.
He harbored astonishing talent within him.
At night, training paused.
Tanjirou couldn't find Zenitsu in the house, and following the scent, he found Zenitsu curled up in the furthest corner of the veranda, seemingly still fearful from the day's terrifying training.
Tanjirou walked over and silently handed him a rice ball he had brought.
This was one of the rations Cheng Mo had prepared, made with substantial ingredients to quickly replenish energy.
Zenitsu froze for a moment, lifted his somewhat red and swollen eyes from crying, and looked at the rice ball.
He then looked at Tanjirou's gentle face, hesitantly took it, and began to eat it in small bites, occasionally letting out a sniffle.
Tanjirou sat next to him, looking at the stars in the sky, and gently spoke: "Zenitsu, you're actually... very strong, aren't you?"
Zenitsu's eating movements suddenly stopped, and his body stiffened.
Tanjirou continued: "I felt it today, under the waterfall, even though you were crying the whole time, your breathing, and your sword-swinging movements, were all very, very impressive."
Upon hearing this, Zenitsu's mouth drooped, and he looked like he was about to cry again: "What's so impressive... I, I only know First Form, I can't learn any other sword forms! Grandpa taught me so many times and I still can't learn them!"
"I'm just a useless good-for-nothing! Grandpa... he must be so disappointed in me..."
As he spoke, his voice carried genuine frustration and self-loathing.
Tanjirou turned his head, looked at him seriously, and shook his head: "No, I don't think so. Precisely because you only know First Form, yet you can practice it to that extent, that's what makes you a true genius."
He added, relying on his keen sense of smell, "Moreover, although Mr. Kuwajima is very strict during training, I can feel that when he looks at you, there is only concern and... worry in his eyes."
He smelled the deep emotions hidden beneath that stern exterior.
Zenitsu fell silent, lowering his head, forgetting to eat the rice ball in his hand. After a long while, he murmured in an almost inaudible voice: "...What do you know, Thunder Breathing... it's too fast, too terrifying... every time I use Thunderclap and Flash with full power, I feel... I feel like my heart is going to burst out, my body is going to shatter... like I'm going to die the next second..."
This was the first time he had revealed to an outsider his deep-seated fear of Thunder Breathing, of that extreme speed.
It wasn't mere timidity, but a genuine tremor at the edge of his own power spiraling out of control.
Tanjirou thought of his sister Nezuko, his gaze becoming even more resolute, and he said forcefully:
"But, Zenitsu, you must have someone you want to protect, right? For the sake of important people, no matter how scared we are in our hearts, no matter how much our bodies hurt, we must become stronger."
"Only by becoming stronger can we protect what we don't want to lose, I... that's how I think."
After this brief late-night conversation, the relationship between the two seemed to subtly draw closer.
Although Zenitsu still cried and complained the loudest during training the next day.
But occasionally, he would secretly and quickly glance at the young man next to him, with a scar on his forehead and eyes burning with fiery dedication to his practice...
Kuwajima Jigorō spared no effort in teaching Tanjirou, the disciple Cheng Mo brought, holding nothing back.
During breaks in training, the old man personally demonstrated the various sword forms of Thunder Breathing for Tanjirou.
Despite his advanced age and disability, when the old man gripped his sword hilt, his aura instantly became like a drawn blade.
In the clearing, the old man stood firm and took a deep breath.
His originally somewhat hunched body instantly straightened, and a sharp, thunderous aura erupted.
"Watch closely, Tanjirou! This is Thunder Breathing!"
He let out a low roar, and his figure suddenly moved!
"First Form: Thunderclap and Flash!"
His figure transformed into a golden streak of lightning, instantly covering a distance of over ten meters.
Where the blade pointed, the air let out a sharp, explosive roar.
"Second Form: Rice Spirit!"
The sword light was like countless electric snakes suddenly rising in the sky, wildly dancing and tearing apart everything in front of it.
"Third Form: Thunder Swarm!"
The afterimages generated by high-speed movement seemed to transform into multiple clones, launching swift consecutive slashes simultaneously from different directions... until the final "Sixth Form: Thunderclap and Flash Continuous!"
Kuwajima Jigorō's figure seemed to transform into actual falling lightning.
Violent thunderous blade energy raged, shattering the distant boulders used as targets into charred fragments!
His movements were as swift as lightning, as powerful as a thunderclap, perfectly embodying the essence of Thunder Breathing.
"The essence of Thunder Breathing lies in extreme concentration and break out! Condensing all mental, physical, and breathing power into a single instant! Like lightning tearing through the night sky, destroying all obstacles in its path!"
Kuwajima Jigorō's roar carried a hint of imperceptible panting.
It intertwined and echoed through the valley with the sharp whistling and faint sounds of wind and thunder created by his sword swings.
Tanjirou's eyes widened, eagerly observing and learning, striving to engrave every detail into his mind.