Chapter 187: Teaching the Secret Arts
Early morning sunlight filtered through the trees as Mugetsu stood at the familiar Training Ground, facing his gathered disciples.
"We won't be taking any D-Rank missions for the next few days," Mugetsu announced, his tone calm but firm. "Instead, we'll focus entirely on training — on strengthening ourselves."
With the rewards from D-Rank missions steadily decreasing, and the recent acquisition of Armament Haki, Mugetsu had decided it was time to push his team's overall power higher.
He continued, "Today, we won't be training here. We're changing locations."
Now that a solid level of trust had been established with Kakashi, Mugetsu planned to return their training site to the South Border Forest — a place more suited for his teaching methods.
Since Mugetsu began taking interns, Rin and Shisui had been training under his Shadow Clones, meaning they didn't benefit from his direct Teaching Skill bonus. Now that everyone would be training together, Mugetsu intended to maximize efficiency — every student would receive the full benefit of his instruction.
Kakashi offered no objection. To him, moving training locations was standard practice; different terrains honed different skills. It was the reason Konoha had so many specialized training grounds — to prepare shinobi for any situation.
Obito, however, was brimming with curiosity. "Where are we going to train? Outside the village? Are you gonna teach us a new secret Ninjutsu, sensei?" His eyes sparkled with anticipation.
"Not outside the village," Mugetsu replied. "We'll be training in the South Border Forest. But yes — I'll be teaching you all a secret technique today."
Obito's excitement spiked instantly. "A secret technique? What kind? Is it that Fire Release move you used before, Mugetsu-sensei?"
"It's not Fire Release," Mugetsu said, shaking his head.
Obito's enthusiasm dimmed slightly, but he was still eager. The fact that Mugetsu had said "you all" meant he would get to learn it too.
Kakashi, meanwhile, focused on the phrasing. "A secret technique…"
He understood the weight behind those words. A secret technique wasn't just any Ninjutsu — it was one guarded closely, passed down only to trusted individuals or clan heirs. The Ino–Shika–Chō trio were perfect examples.
But to be more precise, clans weren't powerful because they had secret techniques; rather, having a secret technique was what allowed them to become clans in the first place.
Kakashi thought back to his father. If he mastered Sakumo's swordsmanship to its peak and passed it on, over generations it too would become a family secret art.
He glanced at Mugetsu thoughtfully. I've never heard of any powerful shinobi with the name Mugetsu. Could it be… this technique is his own creation?
The idea wasn't far-fetched. Mugetsu's strength was extraordinary — far beyond most Jonin. During their last mission, he had effortlessly handled powerful enemy shinobi, even leaving a few Chunin alive for his students to practice on.
In Kakashi's mind, even if Mugetsu hadn't reached the level of the Sannin yet, he couldn't be far from it. For someone his age, that was nothing short of monstrous genius.
With power and intellect like that, developing a secret technique of his own was entirely possible.
Beside him, Might Guy scratched his head. "A secret technique… should I really be learning that too, Mugetsu-sensei?"
He wasn't lacking in confidence — but he was realistic. His self-assurance came from perseverance, not natural talent. When it came to Ninjutsu, even he admitted he was hopeless.
"You must learn it," Mugetsu said seriously. "And you must master it. This will be vital for your future — just as important as Rock Breathing."
Might Guy froze for a moment, then his eyes widened. He understood instantly.
Rock Breathing had completely transformed his training — improving endurance, strength, and even his explosive power. It could also synchronize perfectly with the Eight Gates. If this new technique carried the same weight… it could change everything.
"I understand!" Guy said with uncharacteristic solemnity. "I'll definitely master it!"
Mugetsu gave a faint smile.
---
The group set off toward the South Border Forest, where Shisui and Rin were already deep in training under the guidance of Mugetsu's Shadow Clones.
"Mugetsu-sensei!" Shisui noticed the approaching group first. Sensing no attempt to conceal their Chakra, he immediately stopped his drills and greeted them respectfully.
Mugetsu nodded in acknowledgment, his expression calm and approving.
Rin, who was practicing her monstrous strength technique nearby, also noticed them after hearing Shisui's call. She withdrew her fist — though not before her last strike shattered the massive tree in front of her.
The great trunk creaked and collapsed with a heavy thud. Rin brushed the dust from her gloves, smiled warmly, and waved. "Good morning, everyone."
Kakashi's eyes widened slightly.
That tree wasn't small. Seeing Rin standing there with her usual gentle smile while a tree twice her size lay split beside her… was disorienting.
"Rin's… strength is really that high?" Kakashi thought, recalling his academy memories. He had never seen her exhibit that kind of power before.
Obito, however, was unfazed. He'd seen it too many times already.
He smiled brightly. "Good morning, Rin!"
"That was incredible, Rin!" Might Guy said enthusiastically, flashing a thumbs-up. "So youthful and full of power!"
"The progress is quite good," Mugetsu said approvingly. "But there are still areas you can refine further."
Rin's expression grew serious as she listened intently. Mugetsu's words were always concise yet precise — every sentence carried deep meaning. As he spoke, the mental image of her chakra control technique became clearer, and concepts that had eluded her for weeks suddenly made sense.
"Thank you, Mugetsu-sensei. I feel like everything is much clearer now."
Rin's eyes brightened with understanding as she bowed slightly in gratitude before returning to her training.
Kakashi observed quietly from the side, deep in thought. From the start, something about this setup had puzzled him.
Shisui calling Mugetsu sensei was perfectly natural — he was, after all, a teacher at the Academy. But seeing two of Mugetsu's Shadow Clones supervising training within the village was odd. Shadow Clones were typically used for dangerous missions or reconnaissance, not for ordinary instruction.
As Kakashi watched how precisely Mugetsu guided Rin's movements — and how smoothly Rin responded — the pieces fell into place.
So that's it, Kakashi thought. Rin and Shisui must also be Mugetsu's personal disciples.
With that realization, another possibility surfaced in his mind: Maybe Obito and Might Guy were also taught by him long before this internship began. That would explain their rapid progress.
The more he thought about it, the more it made sense. All of them had attended the Academy around the same time — perhaps Mugetsu had simply taken a liking to them and decided to teach them personally.
---
"Shisui," Mugetsu's voice interrupted Kakashi's thoughts. "Pause your current training for now. Today, I'll be teaching a secret technique."
Shisui, who had activated his Sharingan during practice, immediately stopped and approached Mugetsu's main body. The gleam in his eyes reflected both focus and curiosity.
Given that Armament Haki was tied to Yin Release, Shisui's Sharingan would provide a considerable advantage in learning it.
As for Rin, Mugetsu had no plans to teach her Haki yet. Her current regimen — mastering the Mystical Palm Technique, enhancing her monstrous strength, and refining the Chakra Scalpel — was already enough to keep her occupied for months.
Besides, her Chakra reserves were still too limited to make effective use of Haki. Among all of Mugetsu's disciples, Rin possessed the smallest Chakra pool — barely seven hundred units.
That limitation came from several factors. Her innate reserves were modest, and she had joined Mugetsu's tutelage a semester later than the others. Moreover, unlike them, she lacked a suitable Breathing Technique to boost Chakra efficiency.
For the others, however, the benefits of learning Haki were immense.
Might Guy, once he mastered it, would experience a qualitative leap in both offense and defense — though his learning speed demanded an early start.
Shisui, with his talent and Sharingan, would likely progress the fastest. His natural affinity for shuriken and kunai techniques made Armament Haki an ideal complement.
Obito, as an Uchiha himself, would one day awaken his Sharingan, and right now there was no skill more worthwhile than Haki for his long-term growth.
And Kakashi — his analytical mind and innate control suggested he could learn quickly. His swordsmanship, especially, would rise to new heights once imbued with Haki.
---
"The secret technique I'm going to teach you," Mugetsu began, "is called Armament Haki."
The group exchanged glances. The unfamiliar term hung in the air like a foreign wind.
Kakashi's eyes narrowed slightly. Armament Haki? He'd never heard of such a technique before. That alone convinced him further that it must have been something Mugetsu developed himself.
Mugetsu continued, "You should already know that besides the five basic Nature Transformations — Fire, Water, Earth, Wind, and Lightning — there are also the special Chakra natures, Yin and Yang. This technique belongs to Yin Release."
Guy's expression stiffened immediately. Even the five basic natures were difficult enough for him — the mention of Yin Release made his head spin.
Shisui, however, remained calm. He had already attained a fair degree of proficiency in Yin Release through his prior Genjutsu training under Mugetsu.
"Wow, that sounds amazing!" Obito exclaimed, eyes wide. "Even the name sounds powerful — Haki! It just feels cool!"
Mugetsu raised his right arm, concentrating Chakra into it. Slowly, a deep black sheen began to spread across his skin, until his entire arm looked as though it were encased in obsidian armor.
"This is Armament Haki," Mugetsu explained. "It's a Yin Release transformation that forges a special kind of Chakra — one that can be applied to the body to dramatically enhance both offense and defense."
He turned to Shisui. "Try stabbing my arm with a kunai."
Shisui hesitated, glancing at Mugetsu for confirmation. Receiving a calm nod, he drew a kunai and approached.
The others watched in tense silence as the gleaming blade struck down —
Clang!
The sharp sound of metal meeting metal echoed across the forest. The kunai bounced off harmlessly, failing to leave so much as a mark — not even a faint indentation. Mugetsu's arm remained perfectly smooth, reflecting the morning light like polished steel.
"Use all your strength," Mugetsu said.
Shisui nodded, gripping the weapon with both hands this time. He gathered Chakra, inhaled, and drove the blade down with full force.
Clang!
The impact reverberated through the clearing. The recoil nearly shook the kunai from Shisui's hands.
He took a step back, eyes wide. He had hit with everything he had — yet Mugetsu's arm hadn't even budged.
"Use Chakra," Mugetsu said calmly. "And combine it with Total Concentration Breathing. Then strike again."
"Understood," Shisui replied crisply.
He instantly adjusted his breathing, entering the Flame Breathing state. His breaths became deep and rhythmic, his muscles tightening as his Chakra surged to its limit. The heat of focus radiated from him — the kind only a true Uchiha prodigy could manifest.
With the boost from his Breathing Technique, Shisui infused his Chakra into the Kunai and drove his entire strength into the strike aimed at Mugetsu's arm.
Clang!
The metallic sound rang sharp and clear — but before anyone could check if Mugetsu was hurt, they saw the tip of the Kunai snap clean off and fall to the ground.
Obito's eyes went wide. "That defense is insane!"
Mugetsu's arm hadn't changed at all. The black sheen from the Armament Haki reflected sunlight faintly, not a single mark left behind.
"If this can cover your whole body," Obito muttered in awe, "you'd basically never have to worry about getting hit again…"
Might Guy clenched his fists, realization dawning on him. Now he understood why Mugetsu had told him he had to learn this secret technique.
If he mastered this, even weapons would become unnecessary. He could fight with his bare hands — his body itself would be his weapon.
Kakashi's eyes narrowed thoughtfully. Mugetsu had mentioned that Armament Haki could enhance both defense and offense. He had seen the defense — now he wanted to see what an attack empowered by it could do.
But Mugetsu wasn't finished demonstrating yet.
"Step back," he instructed, signaling everyone to retreat. Once they were at a safe distance, he turned to Shisui.
"Attack me with your full strength using Phoenix Sage Flower Claw Crimson."
The students looked at each other in surprise. To take a Ninjutsu head-on — that was confidence bordering on recklessness.
"Yes, Sensei."
Shisui didn't hesitate. He flipped through a rapid series of hand seals.
"Fire Release: Phoenix Sage Flower Claw Crimson!"
Because Mugetsu had told him to go all out, Shisui didn't use the one-handed Kunai variation this time. He used the full version — weaving signs with both hands and then launching a flurry of flaming Shuriken into the air.
As they cut through the wind, Shisui breathed out streams of fire, igniting each Shuriken into a storm of blazing, swirling fireballs.
Kakashi's eyes widened. "To perform a Fire Release of that level at his age…"
He was genuinely impressed. Back at the Academy, he'd heard Obito brag about a genius named Shisui who was stronger than him — but Kakashi hadn't taken it seriously.
Now, watching Shisui unleash such refined Ninjutsu, he understood. This kid isn't just talented. He's extraordinary.
The flaming barrage tore through the air, each miniature fireball carrying the heat and sharpness of molten steel.
As they approached, Mugetsu exhaled calmly — then poured his Chakra outward, coating his entire body in jet-black Armament Haki.
BOOM! BOOM! BOOM!
The Fire Release struck him head-on. Explosions rippled through the clearing, and blinding fire consumed Mugetsu's figure. The shockwaves tore at the ground, and waves of heat distorted the air.
Obito strained to see through the flames, squinting. Without a Sharingan, all he could make out was a silhouette standing motionless in the inferno.
Then, as the fire died down, Mugetsu raised a hand and casually waved it through the air. A gust of wind burst forth, scattering the lingering smoke like dust.
When the smoke cleared, he stood there unscathed — his dark armor-like coating gleaming faintly under the sun.
"He actually took that head-on…" Kakashi muttered, disbelief flickering in his usually calm eyes.
He had expected Mugetsu to withstand the attack — but not this effortlessly. He had imagined cracks, burn marks, something. Instead, even Mugetsu's clothes were untouched.
That Ninjutsu combined the cutting edge of Shuriken with the scorching power of fire. If it hit a normal Ninja, it would've torn them apart instantly.
Obito's jaw dropped. "That's so cool! This is exactly the kind of Ninjutsu I want to learn!"
He grinned foolishly, his mind already running wild.
Rin's in danger during a mission… I step in, block the attack with Armament Haki, and protect her completely unharmed. Then she looks at me with that admiring gaze and says—
Obito chuckled aloud, lost in his own fantasy.
Mugetsu looked around at his students, his expression calm but proud.
"This," he said, "is the defensive capability of Armament Haki. As long as your mastery is high enough, you can even withstand Ninjutsu directly."
The four listened intently, awe visible in their eyes.
"However," Mugetsu continued, his tone turning serious, "until you reach a certain level of control, don't try to block Ninjutsu with full-body Armament Haki like I did. My strength and Chakra far exceed yours — that's the only reason this method works for me."
He looked directly at Guy. "For most of you, focusing your Haki on one point — a fist, an arm, or a blade — is the proper way to develop it. Concentration leads to perfection."
Then he took a step back, flexing his right hand.
"Now, stand behind me," he said. "I'll show you its offensive power."
The students obediently moved back, watching in silence as Mugetsu began to gather Chakra once again.
The black sheen of Armament Haki enveloped his arm, this time denser and more focused than before. Chakra crackled faintly in the air around his clenched fist.
Everyone's eyes locked on him — Obito's filled with excitement, Kakashi's with curiosity, Shisui's with analytical focus, and Guy's with burning admiration.
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