First mission

In the dense forest of Mount Sagiri, where sunlight could only penetrate through the gaps in the foliage, Haru stood at the edge of a clear flowing river. The sound of the water flowing created a tranquil melody, serving as the backdrop for the training that was about to begin. In front of him stood Urokodaki Sakonji, wearing a wooden mask and traditional kimono, ready to test his disciple's abilities.

"Are you ready, Haru?" Urokodaki asked in a serious tone.

"Ready, Urokodaki-sensei," Haru replied earnestly.

Urokodaki nodded and immediately began to move. He took a deep breath, gathering energy before unleashing his first technique.

"First Form: Surface Slash!"

With agile movement, he directed his sword toward Haru in a swift horizontal slash. The river's water sparkled as if affected by his motion. Haru, already prepared, easily sidestepped, moving his feet as if dancing on the wet ground.

"Good! You're quick, Haru!" praised Urokodaki, his attacks becoming more spirited as if age had no effect on him.

Haru smiled but did not let his concentration waver. He knew Urokodaki was a formidable opponent.

Haru quickly countered with his own technique. "Second Form: Wave of Water!"

This technique was a variation of the second form: Water Wheel, created by Haru by adding chakra to it, generating a destructive force like crashing waves.

He raised his sword, with chakra flowing through it, each of Haru's slashes resembling waves of water surging rapidly toward Urokodaki. With extraordinary precision, Urokodaki dodged, but Haru's slash hit a large rock beside him, sending splinters flying everywhere.

After evading Haru's attack, Urokodaki retaliated, not giving any time for rest. He unleashed a flurry of strikes, each movement of his sword flowing like an unbroken current. "Third Form: River Flow!"

Haru attempted to dodge and block the attacks, but Urokodaki was incredibly fast. Each time Haru managed to evade, he felt the pressure on his body. However, thanks to his extraordinary stamina, he could still move agilely.

"Don't just defend; attack!" Urokodaki shouted, encouraging Haru to be more proactive.

"Understood!" Haru replied.

Haru took a step forward, synchronizing his breath with the flow of water around him. "Fourth Form: Flowing Water!"

He launched an attack that combined speed and precision, but Urokodaki could anticipate his movements. With a swift motion, he launched a counterattack, forcing Haru to evade once again.

As the battle progressed, Haru began to feel fatigue in his muscles. However, this only lasted briefly before the recovery abilities granted by his lineage restored him.

The attacks continued relentlessly. Urokodaki seemed tireless, as if age had no effect on him, but Haru, though panting, kept moving.

"Are you still holding up?" Urokodaki asked, slightly surprised by Haru's endurance.

Haru did not respond and continued to concentrate on the rhythm of his breathing.

Haru regulated his breath, savoring every flow of air that entered his lungs. In each heartbeat, he felt energy coursing through him.

Haru decided to change tactics. He began observing Urokodaki's movement patterns, trying to find a gap in his swift and unpredictable attacks. In an instant, he realized that each of Urokodaki's strikes had a rhythm, and if he could catch that rhythm, he might find an opportunity to strike back.

When Urokodaki launched his next attack, Haru felt his heartbeat resonate with Urokodaki's movements. He stepped softly to the side, evading the sharp slash, and in the same motion, he turned to launch a counterattack. "Fifth Form: The Crushing Wave!"

Quickly, Haru swung his sword, producing a wave of energy that surged toward Urokodaki. The wave created a thunderous sound as it struck the ground, breaking the silence of the forest. However, Urokodaki merely smiled behind his mask, seemingly unaffected by the attack. He easily sidestepped, allowing the wave to pass without hitting him.

Undeterred, Haru continued his assault, each movement becoming increasingly skilled and focused.

Urokodaki, who was continuously observing, occasionally offered light praise but more often urged Haru to be more creative with his attacks.

Haru attempted new variations of his techniques. He combined more random movements with better control. "Sixth Form: Waterfall!"

He swung his sword upward, creating an attack reminiscent of a torrential waterfall, directed at Urokodaki with unexpected power. While his attack looked formidable, Urokodaki remained calm. In an instant, he leaped to the side, using the momentum to redirect Haru's strike.

Haru realized that despite his hard work, Urokodaki always had a quicker response. However, through this process, he learned a great deal. Every failed strike, every evaded movement, added to Haru's understanding of the art of combat. He felt growth within himself, as if he were merging into the flowing current of a river, adapting and moving with it.

After a while, Urokodaki decided to increase the intensity of the training. He unleashed a barrage of strikes at a higher speed, testing the limits of Haru's abilities. Each sword slash came like a raging torrent, and Haru struggled to remain standing. He felt sweat trickling down his temples, but his spirit did not wane as he sensed his power increasing.

Haru focused intently, recalling everything Urokodaki had taught him.

Taking a deep breath, a flow of strength filled him. Haru concentrated chakra in the soles of his feet, and with the dust swept by the wind, his figure suddenly vanished. This was one of the results of Haru's training based on the Shunsin technique from Naruto and Rokushiki: Soru from One Piece. Although, compared to the original techniques, Haru's technique was weaker, it was sufficient for his current needs.

Haru reappeared behind Urokodaki in an instant.

"Seventh Form: Tsunami Wave!"

With a confident motion, Haru gathered all the energy he had and launched a more substantial and powerful attack than before. The wave of energy he created surged with extraordinary strength, as if mimicking the unpredictable force of nature.

Urokodaki, for the first time, looked surprised by Haru's disappearance. Sensing danger, he leaped to the side, but the wave was too powerful to evade entirely. The wave struck the surrounding area, shattering rocks and toppling several small trees.

Haru watched with anticipation as the wave of energy crashed into the earth, altering the landscape around him. However, he had no time to celebrate his success; Urokodaki, though startled, quickly returned to a fighting stance. With remarkable composure, he swung his sword, deflecting the remnants of the wave that had hit, and prepared to continue the battle.

Haru knew he had to capitalize on this momentum.

Urokodaki, with his extraordinary swordsmanship, initiated a rapid counterattack. He swung his sword with precision, each slash purposeful, every movement seemingly measured in a rhythm that was unpredictable. Haru tried to anticipate those attacks, recalling the rhythm he had learned previously.

"Learn to feel," Urokodaki's voice echoed in Haru's ears, urging him to stay focused.

Haru regulated his breathing, feeling his heartbeat quicken. He tried to block out all sounds around him, wanting only to hear the clash of swords. With calm movements, he began to maneuver, using small steps to evade Urokodaki's strikes.

With increasing accuracy, Haru sought a gap in Urokodaki's defense. Each time Urokodaki attacked, he dodged gracefully, trying to close the distance for a counterattack. He seized every opportunity, every small mistake his opponent made. In the midst of the fight, Haru began to feel that he was getting better at reading Urokodaki's movements.

Urokodaki, who continued to apply pressure, started changing his strategy. He switched to faster and more aggressive attacks, trying to force Haru into making a mistake. However, Haru remained calm, striving not to be influenced by the speed of his opponent.

One after another, Urokodaki's attacks came. Haru dodged nimbly, moving like flowing water.

The fight continued for quite a while until it paused as Haru's Kasugai crow circled in the sky.

"Caw... Caw... Caw... Mission... Mission... Kasugano Haruka, please hurry to the south. Many people are missing, suspected to be the work of a demon..."

"Caw... Caw... Caw... Mission... Mission... Kasugano Haruka, please hurry to the south. Many people are missing, suspected to be the work of a demon..."

"Caw... Caw... Caw... Mission... Mission... Kasugano Haruka, please hurry to the south. Many people are missing, suspected to be the work of a demon..."

"Finally, I can undertake my first mission and experience a real fight," Haru said with anticipation about his first battle after learning Water Breathing.

"Haru, be careful. I know with your current strength, an ordinary demon won't be your match. But don't be careless; many demons have strange abilities," Urokodaki warned Haru seriously.

"I understand, Urokodaki-sensei. Thank you for teaching me all this time," Haru replied before bowing with gratitude.

"Be careful on your journey," Urokodaki said before turning and walking back toward his home.

Haru quickly packed his belongings before setting off to the south. He didn't carry much, just a change of clothes, food, and his Nichirin sword.

...

Carefully, he stepped into the darkness of the forest.

Tall trees towered overhead, and the moonlight struggled to penetrate the thick branches. The eerie silence of the forest became increasingly oppressive.

Using the Shunshin technique, he jumped from one branch to another, trying to sense any changes in the energy around him.

Haru continued to move, catching the scent of blood; he immediately approached the source of the smell.

After a while, Haru saw the shadow of the demon in the distance. He slowed his pace and approached cautiously. In the silent forest, he could hear a crunching sound, like something hard being chewed.

Taking a few more steps, he hid behind a tree and could see the tall, slender figure of the demon. It seemed to be enjoying its dinner, completely unaware of Haru's presence.

Haru held back his nausea as he watched the demon bite and chew on a human hand.

Taking a breath with a specific rhythm, as the air filled his lungs and circulated throughout his body, Haru felt a significant boost in power. Along with the Shunshin technique, he vanished from his spot.

"First form: Surface Water Slash"

Haru appeared suddenly behind the demon and launched a horizontal slash towards its neck.

Sensing danger, the demon jumped forward without hesitation. Due to the demon's quick reaction, Haru failed to decapitate it, only managing to slice off one of its hands, which was inconsequential for the demon. In an instant, the severed hand began to regenerate.

With pale skin and sharp red eyes, the demon scrutinized Haru closely.

"Ah, a Demon Slayer," the demon said, its voice hoarse and taunting.

Haru also observed the demon and noticed the markings on its eyes reading "Kagen" and "san." This meant that the demon in front of him was a member of the Twelve Kizuki Lower rank 3.

He had not expected to face a Twelve Kizuki on his first mission. Confronting a Twelve Kizuki, Haru had to be cautious. He didn't know how his strength compared to the demon before him, but he wasn't afraid because he believed in his abilities; if he couldn't defeat it, he could safely retreat.

"Second form: Water Wheel"

Haru ran quickly towards the demon, leaping and spinning in the air; he executed a vertical sword slash like a gracefully rotating water wheel. Though this movement was beautiful, behind its elegance lay a cold blade that brought death.

The reason Haru didn't use Shunshin at this moment was to perform a surprise attack to potentially kill the demon in one blow.

Relying on his speed, the demon, Wakuraba, dodged Haru's slash.

"Blood Demon Art: Iron Skin"

Wakuraba activated his blood demon art, hardening his skin like iron. He quickly approached Haru.

(Note: author does not know Wakuraba's original blood demon art.)

... Boom...

Wakuraba's powerful fist struck the ground as Haru dodged his blow. Wakuraba spun his body and executed a spinning kick. Haru, with no time to react, blocked Wakuraba's kick with his Nichirin sword. Due to the strong friction with the Nichirin sword, Haru's hand began to peel.

Haru glanced at his hand, which was slowly healing under the power of Mokuton's self-healing.

Haru looked at Wakuraba seriously; it seemed that without using Shunshin, he couldn't match Wakuraba's speed.

While Haru battled Wakuraba, his Kasugai crow reported the appearance of the Twelve Kizuki and requested assistance.

Kagaya Ubuyashiki, upon receiving the news, promptly called for the nearest Hashira to provide support. Only Hashira-level Demon Slayers could confront the Twelve Kizuki.

Haru regulated his breathing, feeling his heartbeat racing. Without taking his eyes off Wakuraba, he prepared for his next move.

Wakuraba, not giving him time to ponder, launched another attack. With incredible speed, he leaped toward Haru, his fist aimed directly at his face. Haru dodged, but not quickly enough; Wakuraba's punch flew so close that the fierce wind from the attack nearly knocked Haru back. In an instant, Haru spun, attempting to retaliate with a sharp slash.

However, Wakuraba was already prepared. With agile movements, he parried Haru's attack using his arm covered in iron skin. The sharp clanging sound filled the air as the Nichirin sword met the demon's skin. Haru felt a sharp vibration through his hand, but he did not give up. He continued to attack, changing the direction of his slash, trying to stab at Wakuraba's side.

Wakuraba jumped again, easily evading the strike.

"You'll have to be faster if you want to defeat me," he said mockingly while floating in the air. Haru was not swayed by his words. He knew that in a fight like this, every word would only distract him.

Noticing that Wakuraba continually evaded his attacks, Haru decided to change his strategy. He needed to bait the demon into attacking, then change the speed and direction of his own attacks as quickly as possible. With measured movements, Haru stepped back, creating distance between them.

Wakuraba, feeling confident, seized the opportunity to attack. He lunged forward, his fist ready to strike. Haru prepared himself, chakra gathering in the soles of his feet.

When Wakuraba was within range, Haru moved quickly, utilizing the Shunshin technique to disappear from sight.

Wakuraba was taken aback, unable to find his target. However, as he turned, Haru appeared from behind with an attack gathered from his previous power. "Fourth form: Striking Tide"

Haru unleashed a flurry of consecutive slashes. His Nichirin sword cut through the air at high speed, aimed at Wakuraba's neck.

But the demon showcased his abilities once more. With quick reflexes, Wakuraba raised his arm, deflecting Haru's attack. The loud clang echoed again, and Haru felt a stronger vibration this time. Without waiting any longer, Haru jumped back, planning his next move.

Haru knew he needed to strategize better. He observed Wakuraba's movements, looking for an opening to strike. The demon seemed increasingly confident, believing Haru couldn't match his strength. In his mind, Haru plotted a combination of attacks that would leverage speed and precision.

Suddenly, Haru feigned an attack from the front, but at the last moment, he veered off to the side, attempting to strike the demon's left side. However, Wakuraba was already prepared, and with a swift motion, he turned his body, directing a kick toward Haru.

Haru felt the rush of wind as the kick flew past his head. He quickly jumped back, spinning his body like a whirlpool.

"Sixth form: Whirlpool," he thought.

The spinning slash, like a whirlpool, immediately struck Wakuraba, who was caught off guard, leaving a scar on his unprotected skin.

Haru felt a glimmer of hope upon seeing that Wakuraba couldn't cover his entire body with iron skin. This meant that as long as his slashes were fast enough and struck Wakuraba before he could defend, it might be possible to defeat him.

Quickly, he seized the moment to launch a consecutive series of attacks. He charged forward, slashing with rapid movements, trying to put more pressure on Wakuraba. Each slash felt increasingly accurate, forcing the demon to retreat.

However, Wakuraba did not remain idle. With his power, he tried to parry Haru's attack again, but this time, Haru had anticipated the movement. He leaned his body, pretending to attack from one side, then turned and thrust from the other side.

The attack was successful! Haru's Nichirin sword pierced Wakuraba's skin, though not deeply. The demon let out a cry of pain, but quickly, the wound began to close. Haru had to retreat, realizing that every attack he made needed to be more lethal.

Wakuraba, now looking angrier, activated his blood demon art with greater intensity.

"You will pay for that!" he shouted, his voice filled with rage. With increased power, Wakuraba launched a series of relentless attacks, fists and deadly kicks flying towards Haru.

Haru did his best to evade. He knew that if even one attack landed, it could be fatal. In swift movements, he jumped, rolled, and deflected Wakuraba's strikes, but the force of the attacks felt increasingly stronger. His sword felt heavier, and his arms began to tire. However, every wound he received would soon heal slowly thanks to Mokuton's power, so even though he was often hit by Wakuraba's attacks, there were only a few wounds left, and they were already in the process of healing.

Haru felt the pressure rising. He had to find a way to stop this demon before it was too late. In an instant, he launched a counterattack, using the Shunshin technique to disappear and reappear beside Wakuraba, trying to create a surprise attack once again.

But Wakuraba was ready. He quickly turned, lifting his leg to kick Haru right in the stomach. Haru felt a painful impact, causing him to fall. Quickly, he rolled, trying to get back on his feet.

However, Wakuraba did not give him a chance. He jumped up, intending to crush Haru with a powerful kick. Seeing Wakuraba's attack approaching, Haru, who had just gotten up, hurriedly jumped.

"Tenth Form: Constant Flux"

Haru moved toward Wakuraba, launching a flowing attack with his sword. Instantly, Haru's speed increased along with the accumulation of the technique.

At the last moment before the technique was complete and as Haru stood in front of Wakuraba, he suddenly used Shunshin to shift positions behind Wakuraba.

"First Form: Surface Water Slash"

As soon as he appeared, Haru immediately slashed at Wakuraba's neck, which had not yet reacted.

Wakuraba's head flew high into the sky, his eyes wide open in shock. The head quickly turned to smoke before touching the ground.

Haru sat panting on the ground, watching the transparent panel in front of him. In the bottom right corner, a countdown timer continued to run.

Haru could only remain in this world for a maximum of one year before he would be teleported back to the reincarnation tower.