A Nichirin Blade Bearing Regret, and the Fusion and Advancement of Azure Flow Breathing Style

Time flew. More than half a month had passed since Moyu created his unique Breathing Style, Azure Flow Breathing. Winter had come to Mount Sagiri, bringing biting winds, but the training ground was no less heated for it.

That day, Sakonji Urokodaki summoned Moyu and Tanjiro before him. He held two sheathed Nichirin Blades, both in dark blue scabbards that gave them a solemn air.

"The Final Selection will be held in seven days." Urokodaki's voice came through his Tengu Mask, calm and even, yet it made both boys' hearts leap. "These two Nichirin Blades were not made for you. They are keepsakes left behind by my former disciples..."

Moyu and Tanjiro's expressions grew solemn. Their eyes fell on the fox masks in the clearing, and they understood. Tanjiro's eyes reddened, and his hands clenched involuntarily.

"A true Nichirin Blade is earned by passing the Final Selection. The Demon Slayer Corps provides special ores, Crimson Red Iron Sand and Crimson Red Ore, and an elite smith from Swordsmith Village forges them into a blade. Its color changes according to its user, making it a blade unique to them." Urokodaki handed a sword to each of them. "These two are standard blue blades. Use them for the trial for now. Treat them well, and do not disappoint their former owners' wills."

"Yes!" Moyu and Tanjiro answered together, solemnly accepting the Nichirin Blades. The swords felt heavy in their hands, and beneath their cold touch, they seemed to sense a trace of unwillingness and hope. Moyu brushed his fingertips over the faint wear on the sword guard. His Six Eyes seemed to "hear" the past contained within the blade—the rhythm that resonated with Water Breathing, and... a lingering trace of regret. He wondered if this might be the sword Sabito had once used.

[Ding! Temporary weapon "Nichirin Blade" obtained.]

[Side quest triggered: "Inherited Will": Slay demons with this blade during the Final Selection to console the deceased. Reward: Gold coins awarded according to the number and strength of demons killed, and increased resonance with the Nichirin Blade.]

The system's notifications sounded at just the right time. Moyu gathered his thoughts and secured the sword at his waist. It was time to test the results of his training over the past few months.

"Tanjiro, Moyu," Urokodaki said in a low voice. "For the final seven days, you will spar under combat conditions. Your goal is to last against me for the time it takes one incense stick to burn. Moyu, you may not use your special abilities. Tanjiro, you may not use Sun Breathing."

Before he finished speaking, Urokodaki vanished from where he stood like a phantom. An overwhelming pressure instantly blanketed the training ground: the killing intent of a former Water Hashira who had fought countless battles.

"Left!" Tanjiro's keen sense of smell let him sound the warning first. At the same time, he drew his Nichirin Blade. Water Breathing, Second Form: Water Wheel! He spun, his flashing blade forming a circular curtain of water to protect his side.

Almost as soon as Tanjiro spoke, Moyu's Six Eyes caught Urokodaki's movements. Rather than block head-on, he shifted his footwork, using the technique he had created by incorporating the principles of Shave into his Breathing Style: Azure Flow Breathing: Footwork: Flowing Cloud! He drifted backward like mist and clouds, narrowly avoiding a knife-hand strike from Urokodaki's left. The strike carried the concentrated power of a Breathing Style, and even without a real sword, it cut sharply through the air. (Hey, author, isn't the protagonist cheating? How can he use Shave without buying the Six Styles? The protagonist is a shut-in, and the anime explains the principles behind the Six Styles. He only used them as a reference for the fusion.)

"Good reactions," Urokodaki said approvingly, but his assault never let up. No longer confined to one side, he darted rapidly between the two, at times crashing down like a waterfall, at others winding around them like a stream, displaying Water Breathing's flexibility and versatility to the fullest.

Tanjiro pushed Water Breathing to its limits, using the First Form, Third Form, and Fifth Form in succession. His sword strokes formed a dense defense as he fought to hold Urokodaki off. His fundamentals were exceptionally solid. With the rhythm of the kagura dance incorporated into them, in particular, his breathing was long and steady, and his strength endured, allowing him to barely withstand Urokodaki's storm of attacks.

Moyu took a different approach. With his Six Eyes fully active, he precisely anticipated the trajectory and force of each of Urokodaki's attacks. Rather than frequently use the three highly taxing Zero Form techniques, he relied on the ten forms of Water Breathing, occasionally incorporating the insight and fine control of his Six Eyes.

When Urokodaki slashed at Tanjiro, Moyu moved at the moment the older man's first burst of strength had just run out and the next had yet to begin. Water Breathing, Seventh Form: Drop Ripple Thrust! He and his sword seemed to become a straight line of water, thrusting directly at what appeared to be Urokodaki's only opening: his elbow joint. The strike was exceptionally fast, its timing tricky.

Yet Urokodaki seemed to have eyes in the back of his head. He flipped his wrist and knocked backward with his sword hilt, striking Moyu's sword tip precisely. Clang! A crisp sound rang out, and Moyu felt a deft force divert his thrust slightly, sending it past Urokodaki's sleeve.

"Excellent perception, but your control over your strength still needs work." As Urokodaki gave his assessment, he held the fingers of his other hand together like a blade and struck at Tanjiro's ribs.

Tanjiro couldn't dodge in time, and the blow was about to land. Blue light flashed in Moyu's eyes, and the fingertips of his left hand moved almost imperceptibly. Azure Flow Breathing, Zero Form: Myriad Mimicry! He did not change the form of an object. Instead, he made a wisp of breathing Cursed Energy mimic the sharp sensation of a needle prick and sent it across the air at Urokodaki's wrist.

Urokodaki frowned slightly, apparently sensing the faint but highly threatening energy, and his attack faltered for a moment. Tanjiro seized that instant and leaped backward, avoiding the blow.

"Not enough combat experience, and your coordination is unpracticed." Urokodaki stopped attacking and looked at the two slightly winded boys. "Tanjiro, you focus too much on your own defense and neglect coordination with Moyu. Moyu, your intentions when attacking are too obvious and easily seen through. In a real battle, especially when you may face attacks from all sides in the future, you need both mutual understanding and cunning."

Both boys were ashamed, knowing their teacher's words were true. They had never fought in actual combat and naturally had little fighting experience. Although their daily training had given them a basis for working together, they truly found it difficult to understand each other's intentions in high-speed combat.

"Again!" Urokodaki barked, launching another attack.

Over the next few days, they sparred like this every day. Under Urokodaki's "polishing," Moyu and Tanjiro improved rapidly. They began trying to work together: Tanjiro took the defensive role, confronting their opponent head-on with his tenacious will and increasingly refined Breathing Style, while Moyu moved around in support, using the insight of his Six Eyes to find openings and launching surprise attacks with the unpredictable Azure Flow Breathing.

Moyu also found time to use the Ability Fusion Ticket and some of the gold coins he had received from the system.

[Exchange confirmed: Nen: Four Major Principles (2,000 gold coins).]

[Using Ability Fusion Ticket to fuse and optimize the Four Major Principles of Nen and Azure Flow Breathing Style...]

[Fusion successful! Azure Flow Breathing Style advanced: Energy control precision increased by 50%, mental energy recovery speed increased by 30%. "Ten" can strengthen physical defense, "Zetsu" can effectively reduce the daily burden of Six Eyes, "Ren" can briefly unleash a burst of breathing Cursed Energy, and the properties of "Hatsu" combine with "Myriad Mimicry" to give energy greater malleability.]

The fused Azure Flow Breathing Style brought Moyu's control over energy to another level. He could even imitate the rhythm of Tanjiro's Hinokami Kagura, causing an occasional streak of searing light to flicker through his azure breathing Cursed Energy. Though it was far inferior to true Sun Breathing, it added another variation.

The seventh day was also the day before they would set off for Mount Fujikasane.

In the light of the setting sun, Sakonji Urokodaki looked at the two boys before him, so different in bearing. Tanjiro's gaze was as resolute as a rock, and the aura around him was warm and weighty. Moyu, by contrast, was calm as still water. His azure eyes were unfathomably deep, and the occasional glint within them revealed something extraordinary.

"Tomorrow, you will go to Mount Fujikasane." A barely perceptible note of emotion entered Urokodaki's voice. "The rules of the Final Selection are simple: survive for seven days on a mountain infested with demons. The demons imprisoned there cannot come into contact with sunlight, but many of them are vicious. You must not let your guard down."

He paused, his gaze sweeping over the fox masks. "Come back alive. Not only for yourselves, but for everyone who is hoping for your return."

"Yes, Master Urokodaki!" The two bowed, their voices firm and strong.

That night, Moyu went alone to the waterfall behind the mountain. He drew the blue Nichirin Blade, its surface gleaming faintly in the moonlight. His Six Eyes could clearly "see" the tiny energy channels within the blade, marks left by its long resonance with Water Breathing.

He gently swung the long blade, Azure Flow Breathing Style circulating naturally. He unleashed Vortex Slash, and the spinning force tore through the water. Yet the path of the blade also carried a peculiar smoothness, quietly directing the spray aside. It had incorporated the principles of control from Mirror Dissection. His sword stroke changed, sweeping across a rock by the bank, and a cut as smooth as a mirror appeared silently on its surface.

"Still not proficient enough." Moyu lowered his sword and stood there, silently considering how to link the three techniques more smoothly. He could feel the blade slowly adapting to his breathing Cursed Energy. An extremely faint, starlike azure sheen seemed to shimmer on its blue surface.

[Resonance with temporary Nichirin Blade: 15%.]

The system notification showed that he was on the right path.

Just then, Tanjiro came over as well, carrying a wooden box, his face slightly uneasy. "Moyu, I'm a little worried about Nezuko... and whether I can pass the trial myself."

Moyu looked at him and smiled faintly. "Tanjiro, do you remember the determination you had when you cut through that boulder? Trust your nose, trust your sword, and above all, trust your desire to protect Nezuko. Our training on Mount Sagiri won't have been in vain. Nezuko is here with our teacher; he'll take good care of her."

Tanjiro looked into Moyu's calm, confident azure eyes, and his unease gradually faded. He nodded firmly. "Yeah! We have to pass the trial together!"

The moonlight stretched their shadows long, blending them into the mountain forest. Azure eyes and a crimson heart were about to face the trial of the demons' dark domain together. And far away on Mount Fujikasane, at the edge of Six Eyes' perception, an unusual evil aura mixed with savagery did indeed hang in the air, just as Sabito and Makomo had said.