For a moment, Rengoku Kyojuro was utterly stunned by Kazuki's situation.
He had met many people within the Demon Slayer Corps, but without exception, all of them only came into contact with Breathing Techniques after joining the Corps. Even then, reaching the level of Total Concentration Breathing: Constant required at least several months of arduous training. Yet Kazuki's starting point had already reached what was the end goal for many others.
"In that case," Rengoku said, "I'll directly demonstrate the sword techniques of Flame Breathing for you. Try to see if you can activate a sword form using Breathing Techniques. At this point, all you need to focus on is refining sword techniques and tempering your body!"
As he spoke, Rengoku took two bamboo swords from the weapon rack at the training ground and handed one to Kazuki.
"Yes! Rengoku-sensei!" Kazuki replied obediently in a loud voice. Holding the bamboo sword, he stood to the side and carefully observed Rengoku's movements.
During the past few days with Rengoku, Kazuki had noticed that his hearing wasn't particularly sharp, so he consciously spoke a little louder whenever addressing him.
"First is Flame Breathing, First Form—Unknowing Fire! A technique that launches a sudden charge with an explosive burst of flames!"
As Rengoku explained, he demonstrated the move. He adjusted his breathing, planted his right foot, and gripped the sword with both hands.
In the next instant, he shot forward like an arrow released from a bow, then swung the blade in a horizontal slash. A flame-covered arc tore through the air, releasing a sharp whistling sound.
In Kazuki's eyes, every aspect of Rengoku's body during the execution of the technique was crystal clear—
the movement of his lungs as he breathed, the flow of blood, the contraction of muscles—every detail was etched into his mind.
Kazuki planted his right foot, lowered his center of gravity, and gripped the bamboo sword with both hands, assuming the exact same stance as Rengoku had moments ago. His lungs expanded as he drew in air.
"Watch closely—" Rengoku began, turning around.
But his words were abruptly cut off.
"Flame Breathing, First Form—Unknowing Fire!"
Kazuki shouted, and his body shot forward like an arrow loosed from the string. He swung the sword in a horizontal slash, an identical flame-shaped arc tearing through the air.
Rengoku froze in place, swallowing the rest of his sentence.
It was Flame Breathing—an extremely standard First Form.
But the breathing Kazuki used during his push-ups earlier hadn't been Flame Breathing at all. Could it be that he had learned Flame Breathing and the First Form simply by watching me use it once?
That level of talent… it's even more terrifying than Tokito Muichiro, who became a Hashira in just two months.
At that moment, a storm raged in Rengoku's heart. Kazuki's talent had reached a level that defied comprehension.
Meanwhile, Kazuki—who had successfully replicated Rengoku's technique—furrowed his brows slightly. He felt that using the Breathing Technique just now hadn't been completely comfortable, as though something was holding him back. His lungs could have expanded more, drawing in even more oxygen.
"Rengoku-sensei, was my First Form correct?" Kazuki turned and asked.
Rengoku didn't answer the question. Instead, he walked up to Kazuki and said:
"Kazuki, you should participate in this Final Selection as well!"
What he had just witnessed made everything clear. The child before him was a once-in-a-century genius—someone to whom ordinary logic simply didn't apply. What took others one or two years to learn, this boy could grasp after seeing it once.
He was like a child beloved by the gods themselves, all divine favor gathered upon him alone.
"Huh? Didn't you just say it was still too early for me?" Kazuki asked in confusion.
"My judgment earlier was wrong!" Rengoku declared loudly. "With your talent and your current level of Breathing Techniques, passing the Final Selection will be effortless!"
There wasn't a trace of jealousy in his eyes—only joy and heartfelt satisfaction.
Because he knew the Demon Slayer Corps would soon gain another combatant worthy of the Hashira level. That was a blessing not only for the Corps, but for all of humanity in this land.
"Then what about your test for me, Rengoku-sensei?" Kazuki asked.
"There is none!" Rengoku said, crossing his arms proudly. "Your mastery of Breathing Techniques is already on par with mine—perhaps even beyond it. I can't think of any trial worthy of testing you!"
Then he added, "That said, you should still spend the next few days refining sword techniques—developing forms suited to your own Breathing Technique. Of course, I'll also teach you all the sword forms of Flame Breathing. I hope you gain something from them!"
Hearing this, Kazuki felt as though he were in a dream.
Had he… graduated the moment he became a disciple?
"Yes! I'll work hard!" Kazuki answered loudly.
Over the following days, under Rengoku's guidance, Kazuki developed sword techniques suited to his own Breathing Technique. With the aid of the Transparent World, he was intimately familiar with every aspect of his body, allowing his progress to be astonishingly fast.
At the same time, he learned all five forms of Flame Breathing, as well as its ultimate technique—Esoteric Art: Ninth Form—Rengoku.
He accomplished all of this in just six days.
On the morning the Final Selection was set to begin, Kazuki stood at the entrance of the Demon Slayer Corps estate. Beside him stood Tsuyuri Kanao, who would also be participating in this Final Selection.
At Kazuki's waist hung a sword—an extra Nichirin Blade Rengoku had taken from the armory. These blades were typically issued to participants of the Final Selection.
"Rengoku-sensei, I'm heading out," Kazuki said.
"Mm! I believe you'll succeed!" Rengoku called out loudly in encouragement.
Nearby, Kocho Shinobu also gave Kanao a few words of instruction. As always, Kanao responded with a gentle smile.
After exchanging farewells, Kazuki and Kanao set off together toward Mount Fujikasane, where the Final Selection would take place.
Once they were gone, Shinobu turned to Rengoku with a puzzled expression.
"Rengoku-san, is it really alright to let that child participate in the Final Selection right away? Even if you started training him the moment you met him, it's only been a week."
She had been utterly shocked when she learned that Rengoku intended to send Kazuki to the Final Selection. Knowing Rengoku's character, she asked only now.
"There's no problem at all!" Rengoku replied confidently. "That child is a genius! He already has his own Breathing Technique, has developed corresponding sword forms, and has even mastered Flame Breathing—including all its techniques!"
"…You're joking, right?" Shinobu murmured. "Seven days…"
She was completely dumbfounded by Rengoku's words, staring toward the direction where the two figures had disappeared, momentarily speechless.
—
At the same time, inside a small hut on Mount Sagiri, a red-haired boy donned a blue haori patterned with clouds and put on a fox-shaped warding mask.
"I'm heading out, Urokodaki-san!"
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