Two days had passed since Asta began learning Total Breathing Concentration, and he was still in the stage of mastering Constant Breathing.
At this moment, Gabriel was training Asta to get accustomed to applying Total Breathing Concentration under the pressure of a real battle.
In other words: they were dueling one-on-one.
As his weapon, Gabriel wielded his shovel.
On the other side, Asta swung the Demon-Slayer Sword, a replica Gabriel had created from Dark Matter Magic, with weight and balance mimicking the original.
CLANK! CLANK! CLANK!
The clash of metal rang out across the open area in the middle of the forest. Each strike sent gusts of wind whipping through the surroundings, the force of the swings palpable.
Yet Asta struggled.
Not due to a lack of strength—but because he had difficulty keeping up with Gabriel's movements.
Every time Asta tried to read Ki, Gabriel always managed to outmaneuver him.
With Gigan, Gabriel's vision processed the world frame by frame, making every one of Asta's movements appear painfully obvious.
Meanwhile, to Asta, Gabriel's motions seemed to skip between moments he couldn't even perceive.
Amid the chaos, Asta's breathing began to falter. Gabriel's lips curved into a faint, almost Ash-like smile.
"Asta, listen," Gabriel said calmly, "there are a few key points in applying Total Breathing Concentration on the battlefield."
"Y-yes!?" Asta stammered, instinctively slowing down—his reflex urging him to heed his master's guidance.
Slash!
Seizing the opening, Gabriel unleashed a single vertical Scanaiden strike.
Asta's body was hurled back, smashing into several trees behind him and skidding nearly twenty meters.
Gabriel advanced without pause.
Strike after strike rained down relentlessly, forcing Asta to defend while gradually losing his momentum and the rhythm of his breathing.
Between swings, Gabriel's voice remained calm and clear.
"Lesson one. If you focus the flow of power into your legs, maximizing the output of every muscle and blood vessel within—"
He unleashed a heavy strike; the gust of wind from it rattled the ground.
"—your movements will mimic lightning, with incredibly precise accuracy."
Asta chose to block it head-on.
BOOM!
Their blades clashed, and the earth around the impact point sank nearly thirty centimeters, cracks radiating in all directions.
"Ugh…!" Asta groaned softly, feeling his bones creak under the force.
Gabriel landed lightly a few meters ahead, a faint smile on his face, continuing to explain as if teaching a lesson in a normal classroom.
"That's why," Gabriel continued, "a skilled practitioner can make the air vibrate just by preparing a technique—even with a single step."
"That vibration creates a loud sound," he said calmly. "Like thunder."
Before Asta could fully process that—
BAM!
Gabriel's kick struck Asta with full force. His body flew through the air, soaring nearly fifty meters before crashing into a massive boulder.
BOOOOM—!!!
The rock shattered into pieces. Dust and debris shot high into the air, momentarily blocking all sight.
Moments later—
SWOOSH!
A massive swing cleared the dust. Asta's silhouette appeared, standing while resting the Demon-Slayer Sword against the ground.
"Sensei…!" Asta exhaled heavily, sweat streaming down his face. "Giving explanations in the middle of a fight… that's cruel, you know!?"
Gabriel stopped in his tracks, shrugging slightly.
"That wasn't sudden," he replied flatly. "That was Lesson Two and Lesson Three."
Asta blinked. "Huh?"
"Lesson Two," Gabriel continued, "never let your breathing slacken under pressure."
"And Lesson Three—" he exhaled softly, his shoulders lowering slightly, "fighting while thinking is the best form of training."
He then spun the shovel in his hand and rested it on his shoulder.
"That's enough for today," Gabriel said. "You may rest."
Asta stared at him for a few moments, then broke into a wide smile, despite his body feeling thoroughly beaten.
"Sensei's tired too, huh?"
Gabriel gave a small nod. "A little."
The forest fell silent again—leaving only the heavy breaths of two people pushing their limits.
Gabriel and Asta walked toward a leafy tree, beneath which several bottles of drinking water had been placed.
As they walked, Gabriel focused his mind briefly and deactivated the five Compression Energy outputs in his body.
In truth, to outperform Asta in their earlier sparring, Gabriel hadn't relied solely on physical strength.
He had augmented his body with Mana—because purely on physical terms, their abilities were nearly equal at this point.
To avoid making the fight appear one-sided, Gabriel had been forced to use Mana as support.
Moreover, he himself had not truly mastered Total Breathing Concentration—yet Asta had surprisingly felt it on his first attempt.
Once they reached the spot, they sat side by side under the tree.
Each grabbed a bottle and drank in silence, letting their breaths return to normal.
Gabriel turned slightly toward Asta, even though his eyes remained hidden beneath his black bangs.
"Asta," he said calmly. "After this rest, you may head home."
He then shifted his gaze to the sky through the gaps in the leaves.
"Today's training is enough. It's already midday—and besides, I have other matters to attend to," Gabriel said.
Asta finished the last sip from his bottle, then responded eagerly, "Understood, Sensei!"
Suddenly, he froze as if he had remembered something. "Ah!" Asta turned quickly. "Sensei, the technique you explained during the fight—can it really produce a sound like thunder?"
Gabriel tilted his head slightly.
"What do you think?" he replied. "Try it yourself. It's not Magic."
He ended the sentence in a calm but firm tone. "It should be possible without using Mana."
Asta looked at his own hands, then clenched his fists with a determined expression.
"If it's not Magic…" he muttered. "Then it's purely about the body and breathing, huh?"
He stood up, inhaled deeply as Gabriel had taught him, and exhaled slowly. Though the thunderous sound hadn't yet manifested, Asta couldn't help but smile broadly.
"Alright! I'll keep trying, Sensei!" he said enthusiastically. "As long as it's not Magic, I can definitely use it!"
Gabriel nodded slowly. But as his gaze dropped—almost unconsciously—he noticed the weighted bracelets wrapped around both of Asta's arms.
For a moment, there was a brief silence.
"…Oh."
Gabriel's tone was flat, as if he had just remembered something long overdue.
Asta turned to him. "Huh? What is it, Sensei?"
Gabriel tilted his head slightly and spoke casually, as if discussing something trivial:
"Tomorrow, we'll increase the weight."
Asta blinked. "Eeeh…!?"
"The bracelets on both of your arms," Gabriel continued, "will be raised to two hundred kilograms each."
"…Per bracelet?" Asta repeated slowly.
"Yes." Gabriel nodded lightly. "On each arm."
Silence.
"…So the total… four hundred kilos?" Asta asked, with a stiff smile.
"Correct," Gabriel replied succinctly.
Asta's smile tensed for a moment—then transformed into a blazing grin.
"HAHA! Alright, Sensei!"
"If this can make me stronger, I'm all in!"
Gabriel watched Asta for a few seconds, then closed his eyes, a faint, subtle smile lingering on his face.
Ten minutes passed.
The rest period was over.
Asta stood up, dusted off his training clothes, and gave a brief bow. "Thank you, Sensei! I'm heading home!"
Without waiting for a reply, he turned and ran off, his figure gradually disappearing among the trees.
Gabriel remained standing where he was, watching Asta's back until it completely vanished from sight.
A moment later, he straightened up.
His steps carried him behind the dense tree, where a broom rested quietly.
Gabriel grasped its handle and mounted it in a single, fluid motion.
The broom lifted gently, rising from the ground.
The next instant, Gabriel shot through the air, ascending and leaving the forest behind—cutting across the sky in calm silence, as if today's training had been nothing more than a warm-up for something far greater.
***
Seven days had passed.
Now, relying on nothing but explanations and relentless hard work, Asta was already capable of using the Kaminari no Kokyū technique—albeit only Ichi no Kata.
At the moment, Gabriel sat leisurely on one of the branches of a tall tree, an apple resting in his hand.
"Heh," he chuckled softly. "That kid really is a monster when it comes to physical training. If he'd been born in another world… Asta would've become an extraordinary knight."
A faint smile formed on his lips.
"Like a constellation that doesn't follow its proper course," he murmured. "Beautiful… but in the wrong place."
Gabriel took a bite of the apple, then leaned his back against the tree trunk.
His gaze drifted toward the still-dark morning sky, slowly being torn apart by the light of dawn as it pushed the night away.
"But…" he murmured softly. "That's strange. Asta is late. He usually shows up at four in the morning. It's already eight now, and he still hasn't appeared."
Gabriel let out a thin sigh. "I was planning to give him Mizu no Kokyū training at the nearby river today, too."
He then closed his left eye. His awareness shifted, merging with one of the beetles perched among the surrounding trees.
The insect took flight.
However, instead of finding Asta, what entered Gabriel's vision was a black-haired man wearing a tank top and long pants, floating through the air on a broom.
In the man's right hand, a katana was gripped tightly.
___
Author's note:
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