The sun had barely risen over the mountains as the group gathered at the training grounds. The morning air was cool and crisp, but there was an undeniable tension in the air. Today wasn't just any training session—this was preparation for war. And everyone present knew it.
Tanjiro stood beside Gon and Killua, his expression serious but focused. He had trained here countless times before, honing his Water Breathing techniques under the watchful eyes of the Corps' senior members. But today felt different. The weight of the recent battle with Nakime still lingered in the back of his mind, and he knew that the next time they faced an Upper Moon, they would need every ounce of strength they could muster.
Killua's sharp eyes scanned the training grounds, watching the other demon slayers practice their swordsmanship and breathing techniques. "They're strong," he muttered, his voice low. "But are they strong enough to handle Muzan's top demons?"
Tanjiro turned to him, his expression soft but filled with resolve. "The Hashira—the strongest of the Demon Slayer Corps—have faced the Upper Moons before. They're the ones we'll be training with today. If anyone can help us prepare, it's them."
Killua's gaze flickered with interest. "The strongest, huh? I'd like to see what they can do."
Gon, who had been quiet until now, couldn't hold back his excitement any longer. "This is going to be amazing!" he exclaimed, his eyes bright with enthusiasm. "We're going to learn so much from these guys, Killua! I bet we'll get even stronger!"
Killua smirked, though his expression remained cautious. "Just don't get carried away, Gon. This isn't like the fights we've had before."
Tanjiro smiled at Gon's energy, but his thoughts were more grounded. He knew firsthand just how powerful the Upper Moons were—and how deadly Muzan could be. This wasn't just about training. It was about survival.
Suddenly, the sound of footsteps approaching from behind drew their attention. They turned to see a group of figures walking toward them, each one radiating a powerful aura that could only belong to seasoned warriors. At the front of the group was a man with flame-like hair, his piercing eyes filled with confidence and warmth. His presence alone seemed to brighten the entire training grounds.
"Rengoku!" Tanjiro called out, a mixture of admiration and respect in his voice.
Rengoku Kyojuro, the Flame Hashira, gave Tanjiro a broad smile as he approached, his voice booming with energy. "Tanjiro! It's good to see you!" His gaze then shifted to Gon and Killua, his smile never wavering. "And these must be the new warriors from another world! I've heard much about your strength."
Gon grinned, stepping forward eagerly. "We're Gon and Killua! We came through a portal, and now we're here to help fight Muzan!"
Killua, as usual, stood back with his arms crossed, offering a small nod in acknowledgment. He was always wary of new people, especially when they were this powerful.
Rengoku's eyes gleamed with excitement. "I admire your spirit! Anyone willing to stand against Muzan is a friend of the Demon Slayer Corps!" His voice was as warm as the flame he embodied. "Today, we'll begin your training! Prepare yourselves, for it will not be easy."
At Rengoku's words, several other Hashira joined them. Tengen Uzui, the Sound Hashira, stood with his usual flamboyance, while the stoic Giyu Tomioka, the Water Hashira, silently observed the newcomers. Shinobu Kocho, the Insect Hashira, watched with a playful smile, her sharp eyes betraying her calculating nature.
Each of them carried an overwhelming presence—different from Gon and Killua's previous mentors, but every bit as intimidating. There was no question: these were some of the strongest warriors in this world.
"We'll be testing your strengths today," Rengoku explained, his voice booming across the training grounds. "Your abilities may be different from ours, but I'm sure we can learn from each other. And remember, in battle, our goal is to support each other as comrades."
Gon's fists clenched with excitement. He loved learning new techniques, and the idea of training with the Hashira was almost too much to handle. "I'm ready!" he declared, his eyes burning with determination.
Killua's smirk returned, his excitement more controlled but no less intense. "Let's see what they've got."
The Training Begins
The first part of their training was a test of physical endurance. The Hashira watched as Gon and Killua sprinted across the training grounds, dodging obstacles and performing various agility drills that would push their bodies to the limit.
Gon, with his endless energy and tenacity, thrived in the physical challenges. He darted through the obstacles with ease, his body already conditioned from years of training as a Hunter. His speed, power, and relentless drive impressed even the stoic Giyu, whose sharp gaze followed every move Gon made.
Killua, on the other hand, moved with a different kind of grace—faster, more calculated. His Godspeed allowed him to slip through the drills with lightning precision, his movements almost too fast for the naked eye to follow. Tengen Uzui, always drawn to flashiness, couldn't help but admire the young assassin's agility and speed.
"This one's got style," Tengen said, nodding approvingly as he watched Killua dart through the course. "He moves like lightning."
Rengoku grinned, his eyes filled with excitement. "Indeed! Their speed and power are impressive—but the real test will come when they face the demons. Physical strength alone won't be enough."
After the physical drills, they moved on to Breathing Technique training. Tanjiro stepped forward to help guide Gon and Killua through the basics of Breath Control, explaining how the different breathing techniques could enhance their abilities in battle.
"You have to focus your mind and body," Tanjiro explained, his voice calm but focused. "Every breath you take should be controlled. It strengthens your body and sharpens your senses. If you can master your breathing, you can make your attacks stronger."
Gon, always eager to try something new, listened carefully. "So, it's like using nen to control your aura?" he asked, drawing the connection between their two worlds.
Tanjiro nodded. "Kind of. But instead of using your life energy, you're channeling your physical strength through your breath."
Killua, standing to the side, frowned as he focused on controlling his breathing. He wasn't used to this kind of training—it felt different from how he used nen, but he could see the value in it. "If we can combine this with nen," Killua said thoughtfully, "we could enhance our attacks even more."
Rengoku overheard and smiled proudly. "Exactly! If you combine your strengths with ours, we'll become even more formidable. But remember, it takes time and patience to master Breathing Techniques. You must train your body to withstand the strain."
Despite their initial struggle with the breathing techniques, both Gon and Killua adapted quickly. Their intense focus and natural combat instincts made them fast learners. Soon, they could feel their attacks growing more powerful, their movements sharper.
But the Hashira weren't done with them yet.
After several hours of training, Rengoku clapped his hands, signaling the next part of their session. "Now, we'll see how well you fight in a real battle. Tanjiro, you'll be sparring with Gon. Killua, you'll face Giyu."
The group gathered in the center of the training grounds as the pairings took their positions. Gon and Tanjiro stood opposite each other, both of them grinning in anticipation.
"I've been wanting to see how strong you are, Tanjiro!" Gon said, bouncing on his feet. "Let's go all out!"
Tanjiro smiled, his hand resting on the hilt of his sword. "I'll do my best!"
On the other side of the field, Killua stood across from Giyu, his expression unreadable. Giyu, quiet as always, met Killua's gaze with calm intensity.
"I've heard you're fast," Giyu said softly. "Let's see if you can keep up."
Killua's smirk returned, electricity crackling in his hands. "I'll show you fast."
With that, the matches began.
Gon charged forward with his typical unrestrained energy, his fists glowing with nen. "Jajanken: Rock!" His punch shot forward, powerful and full of force. But Tanjiro was ready.
In a fluid motion, Tanjiro drew his sword, his breathing calm and steady. "Water Breathing, Second Form: Water Wheel!" He leapt into the air, spinning with his blade as he redirected Gon's punch, avoiding the full brunt of the attack.
The two clashed, their movements quick and precise, testing each other's limits as they exchanged blows.
Meanwhile, Killua activated Godspeed, disappearing in a flash of lightning as he darted toward Giyu. But Giyu remained calm, his Water Breathing technique flowing like a river as he blocked Killua's attack with ease.
"Impressive speed," Giyu said quietly, his sword meeting Killua's outstretched claws. "But you'll need more than that."
Killua grinned, his eyes gleaming with excitement. "Don't worry—I've got more."
The training grounds erupted in a flurry of movement as the sparring continued, each combatant pushing themselves to the limit. The Hashira watched closely, their expressions serious but filled with respect for the young warriors who had joined them.
And as the sun began to set, the weight of the battles to come hung over them all.