And here, in this world, there were Breathing Styles of various attributes, passed down for millennia— In other words, his right eye's ability was like an enhanced version of the Mangekyo Sharingan's copy-replication. Weak if used poorly, yet overwhelmingly powerful when mastered.
When he had first awakened it, he had glanced at Itachi's Amaterasu, and his right eye had recorded it. But with the Mind Teleporter draining his body of chakra, his right eye had naturally fallen dormant, much like Kakashi's had when he first awakened his Mangekyo. However, being of Uchiha blood, once his chakra recovered and supplied his right eye, its dojutsu power was also restored.
"Damn it! You can't kill us without a Nichirin Blade! Die~!" The female demon, Susamaru, leaped back a distance, roared ferociously, and threw her temari balls. In her hands, these balls possessed the impact force of cannonballs. If a human body were struck, even a glancing blow would obliterate flesh and blood. This was her unique Blood Demon Art, and the balls were made from her blood; she could create as many as she wanted. They were sturdy and resilient. When she cooperated with Yahaba, she was practically a human mobile turret.
Yahaba's invisible telekinetic arrows could control many balls, while she could create and launch them. In this way, countless balls, like cannonballs, would fly around chaotically, being reused repeatedly. As long as they maintained distance, even a Hashira would be defeated on the spot.
Susamaru knew her opponent was formidable and immediately went all out. Her six hands instantly produced six balls, launching them like artillery shells, then immediately conjured another six and threw them again—
Boom...Boom! Boom! Boom!—
The scene was like an attack from a 19th-century artillery squad. Countless immensely powerful temari balls, comparable to iron cannonballs, shot directly towards Tanjiro and Uchiha Nagi. The brick and stone houses shattered like they were made of paper.
[A human artillery turret—] Uchiha Nagi thought to himself. Such destructive power was comparable to an A-rank ninjutsu. A single human cannon could be compared to little Naruto's Rasengan, and now this Susamaru was firing in barrages like a turret... One could imagine a scene with hundreds of Narutos throwing Rasengans, and her speed was more than ten times faster than Naruto's.
Beside him, Tanjiro's pupils constricted. He hurriedly used his Breathing Style sword technique, "Water Breathing, Fourth Form: Striking Tide—Disorderly!" His Water Breathing Style, like a whirlpool, guided his Nichirin Blade, swiftly striking the countless incoming temari "cannonballs." [This won't do! I have to get close to her! Otherwise, if this continues, my stamina will run out, and I'll eventually get hit!] Breathing Styles weren't invincible; they constantly consumed a person's physical strength. Tanjiro could only defend against her heavy balls while trying to close the distance.
"Trying to cut my neck? Hahahaha, dream on!" Susamaru shrieked, using her Blood Demon Art while simultaneously leaping a large distance backward. "You can't escape! Just obediently let me kill you, hahaha!"
Uchiha Nagi easily dodged. His three-tomoe Sharingan was sufficient to evade her attacks, let alone his Mangekyo, which possessed dynamic vision capable of keeping up with the Flying Thunder God Technique. He didn't need to dodge her projectiles; he just needed to avoid the direction her hands were aiming before she threw, much like how dodging a bullet is difficult, but dodging a person's hand is relatively simple. Indeed, a Sharingan with two tomoe or more already possessed the ability to predict an enemy's movements. During Naruto and Sasuke's first battle at the Valley of the End, Sasuke had used his two-tomoe Sharingan to predict all of Naruto's attacks.
Uchiha Nagi dodged while rapidly closing the distance. Just as he was about to get near... A red glint flashed in his crimson dojutsu pupils, and he executed Tanjiro's technique: "Water Breathing, Fourth Form—Striking Tide—Disorderly!"
After their two figures crossed, Uchiha Nagi sheathed his sword. Susamaru, behind him, had a dazed look in her eyes, muttering some kind of crazed laughter. Only when her head fell to the ground did clarity return to her eyes. "Aaaah~ What happened?! Didn't I kill you? How was my head cut off? What's going on?!" Susamaru discovered in terror that her head was separated from her body. Not only separated, but her body had also been dismembered. All six arms and both legs had been severed by him.
Tanjiro, in the distance, froze for a moment, then quickly reacted and shouted, "Be careful! She can't die yet! Demons can't be killed if their necks are cut with an ordinary sword!"
"It doesn't matter." Uchiha Nagi calmly walked to one side and forcefully kicked Susamaru's head away. "Even if she can't die, as long as she's dismembered, she poses no threat. As for her regeneration, I'll just cut her down again." He then used the Great Fireball Technique—which never seemed to actually kill anyone—to burn all of Susamaru's severed limbs.
"Aaaah! How is this possible?! I clearly killed you! How did I end up being the one decapitated?! I don't believe it! I don't believe it~" Susamaru's head shrieked in confusion as it rapidly began to regenerate.
"I used Genjutsu. A Mangekyo's Genjutsu is not something a weakling like you can resist~" Uchiha Nagi calmly walked up to her and explained. The moment he had gotten close to her, the instant their eyes met, she had fallen under his Mangekyo's illusion. The Mangekyo Sharingan inherently possessed Genjutsu capabilities. Even Obito, who wasn't a Genjutsu specialist, could use it to control the Nine-Tails, let alone Uchiha Nagi, who had studied Genjutsu for some time.
"Genjutsu? What's that? I know! It's like Lower Rank One's dream ability! My loss wasn't unjust..." Susamaru muttered to herself.
Tanjiro quickly ran over and struck Susamaru's neck, where two legs were about to sprout, with his Nichirin Blade. As if inherently countered, after her neck was severed by the Nichirin Blade, her head stopped regenerating. Instead, the wound began to burn, turning to charcoal, then to ash. This was the power of a Nichirin Blade—
On the verge of death, Susamaru seemed to awaken memories from her time as a human. A profound sorrow filled her heart. Tanjiro, sensing it, felt a pang of sadness for her. [She's a demon, yet why does she feel so sad...]
"Please... kill me... please..." A weak voice drifted over. It was Yahaba. He was still being burned by Amaterasu. His body's energy was likely depleted. Now, burned down to a mere skeleton, he was immobile but could still speak faintly.
Tanjiro couldn't bear it and was about to walk over and give him a quick end with his Nichirin Blade when he suddenly heard a sorrowful melody. Uchiha Nagi, at some unknown point, had walked over to where Kagome lay, picked up a bamboo flute, and began to play that snowy land bamboo flute song Kagome had wanted to learn—a melody reminiscent of a Naruto BGM.
Tanjiro, drawn in by the gentle sorrow of the music, stopped. Yahaba, struggling in agony, also gradually calmed down. The melody was mournful and captivating, as if guiding a long-lost soul back to their hometown.
When the song ended, the sky was gradually brightening. Yahaba smiled, tears slowly trickling from the corners of his eyes. He remembered his hometown, remembered his home, remembered himself as a human. Then, he stopped struggling and, under the first rays of the morning sun, slowly turned to ash.
Kagome's soul seemed to stand in the sunlight too, smiling. "This melody... is so beautiful..."