In the early morning, Mutsuki met with his disciples at the training ground as usual.
"These days, we won't be taking on missions. Instead, we'll focus on training to enhance our strength," Mutsuki said to his disciples, including Obito and Kakashi.
With the diminishing returns from D-Rank Missions and the acquisition of the powerful Secret Jutsu, Armament Haki, Mutsuki decided to have his students focus solely on training for a period of time.
Mutsuki continued, "Today, we won't be training here at the training ground. We'll move to a different location for our training."
Having established some trust with Kakashi now, Mutsuki decided to change the training location back to the Southern Border Forest.
Since Mutsuki began mentoring interns, Rin and Shisui haven't received any additional teaching bonuses; instead, they've been taught by Shadow Clones.
Since it's all about training, Mutsuki will surely strive to maximize gains, teaching and receiving skill bonuses together.
Kakashi had no objections. Ninja training inherently involves practicing in different places, which is why Konoha has so many training grounds, to provide Ninjas with comprehensive training locations.
"Where are we going to train? Outside the village? Are you going to teach some new powerful Ninjutsu?" Obito asked with curious eyes gleaming.
"Not outside the village, but near the Southern Border Forest. However, there is indeed a Secret Jutsu I will teach you," Mutsuki replied.
"What kind of Secret Jutsu is it? Is it the Fire Release you used before, Yumi-sensei?" Obito's interest was immediately piqued.
"It's not Fire Release," Mutsuki shook his head.
Obito's interest diminished slightly, but he was still excited because indicated that he should be able to learn it too.
"Secret Jutsu," Kakashi detected the hint in Mutsuki's words.
The so-called Secret Jutsu refers to Ninjutsu with very high levels of secrecy. Generally, Ninjutsu referred to as Secret Jutsu are not simple, because if they weren't strong, there would be no need for secrecy.
Konoha has many ninja families that have inherited Secret Jutsu, with the most famous being the Ino-Shika-Cho.
However, it's more accurate to say that Ninja families are more likely to have Secret Jutsu than it is to say that having Secret Jutsu makes a Ninja family.
If he were to master the swordsmanship passed down to him by Sakumo Hatake to the same level as Sakumo Hatake, and then pass it on to the next generation, over time, it would also be considered Secret Jutsu.
Kakashi was a bit curious about where Mutsuki's Secret Jutsu came from, as he hadn't heard of anyone with the surname Yumi being a powerful ninja.
"Could it be something Yumi-sensei created himself?" Kakashi speculated inwardly.
This wasn't entirely impossible, because Mutsuki's strength was truly unfathomable. In the last encounter, the enemies were already considered formidable, yet Mutsuki could effortlessly handle them without needing to take it too seriously, and could even leave a few Chunin for them to practice against.
In Kakashi's mind, Mutsuki's strength, even if it hadn't reached the level of the Sannin, was not far off. Considering Mutsuki's age, this was already a super genius.
With this level of strength at this age, even if Mutsuki were to develop a Secret Jutsu capable of supporting an entire ninja clan, Kakashi wouldn't be too surprised.
"Secret Jutsu, huh? Should I learn it?" Guy scratched his head and asked Mutsuki.
Though Guy was confident, he was confident in his own effort and perseverance.
When it came to Ninjutsu talent, Guy was realistic. He admitted that his Ninjutsu talent was lacking, and if he had the talent for Ninjutsu, he wouldn't have specialized in Taijutsu.
"You should learn it, and you must learn it. It's very important for your future, as important as Stone Breathing," Mutsuki said seriously.
For someone like Guy, who specialized in Taijutsu, Armament Haki was crucial, even if it was just at the Beginner level, as it would enhance his overall potential.
With Mutsuki's words, Guy instantly grasped the importance of that unknown Secret Jutsu.
Guy, who had already grasped the extent of Stone Breathing Beginner's assistance to him, understood its benefits: stronger training effects, greater explosiveness, and the ability to complement Eight Inner Gates.
Next, Mutsuki led his disciples to the Southern Border Forest to train.
When Mutsuki and the others arrived, Shisui and Rin were already practicing under the guidance of Shadow Clones.
"Yumi-sensei," Shisui quickly noticed the approaching group without any concealment, paused his training, and greeted Mutsuki.
Mutsuki nodded and smiled in response.
Rin, who was practicing Enhanced Strength, heard Shisui's voice and also noticed Mutsuki and the others. After breaking the tree she was practicing on with a punch, she too greeted them with a gentle smile.
As Kakashi listened to Rin's cheerful greeting amidst the thunderous sound of the falling tree, and saw her waving with her slender arms, his pupils contracted.
"Was Rin-chan always this strong?" Kakashi recalled his memories from school but found nothing related to this.
Unlike the surprised Kakashi, Obito had already grown somewhat accustomed to it. After seeing it many times, he found it to be normal.
"Good morning, Rin-chan," Obito greeted Rin with a grin.
"That was quite spirited just now!" Guy praised Rin with a thumbs up.
"Your progress is good, but there are still areas where you can improve," Mutsuki nodded and then gestured to Rin.
Attentively listening, Rin quickly visualized Mutsuki's words in her mind, replaying the scene of Enhanced Strength and forming new ideas about areas she hadn't understood before.
"Thank you, Yumi-sensei. Everything seems much clearer now," Rin recalled the moment of inspiration, her eyes shining a bit brighter. She quickly thanked Mutsuki and resumed her training.
Kakashi watched the scene with a pensive expression.
From the beginning, he found it odd that Shisui called Mutsuki "Yumi-sensei," which wasn't unusual since Mutsuki was an Academy sensei. However, having two Shadow Clones of Mutsuki here was quite strange.
Training within the village wouldn't typically require sending two Shadow Clones ahead to scout. After all, the training location would have been decided in advance, not chosen on a whim.
Observing Mutsuki teaching Rin with such proficiency, coupled with Rin's performance, dispelled Kakashi's doubts.
Shisui and Rin must be additional disciples that Mutsuki took on, which is why he brought them here to train together.
Kakashi even entertained a speculation: perhaps Obito and Guy had also become Mutsuki's disciples early on, which would explain their remarkable progress.
After all, both parties were in the Academy; maybe Mutsuki simply took a liking to them and decided to teach them.
"Shisui, temporarily set aside your current training. Today, I'm going to teach you a Secret Jutsu," Mutsuki interrupted Shisui's training.
Shisui had already activated his Sharingan, which, combined with its benefits, made learning techniques related to Yin Release a perfect fit.
Immediately ceasing his training, Shisui walked over to Mutsuki's main body.
Mutsuki currently has no plans to teach Rin Haki. Currently, Rin's training regimen will keep her busy for quite some time—Mystical Palm Jutsu, Enhanced Strength, Chakra scalpel, and so on. Once she's made significant progress in those areas, Rin can start learning Haki.
Because even if Rin were to learn Haki now, it wouldn't be of much use; her Chakra reserves are insufficient. Among Mutsuki's disciples, Rin has the least Chakra, currently only at seven hundred.
There are several reasons for her low Chakra reserves. Firstly, her inherent Chakra capacity is naturally limited; when Mutsuki first assessed her, it was far lower than Guy's and Obito's. Additionally, Rin became a disciple one semester later than Obito and the others, and she hasn't found a suitable Breathing Technique yet.
The reason for teaching the others is different. Guy's learning curve is slower, so the sooner he starts, the better, as mastering Haki will lead to a significant improvement in his abilities.
Shisui already has his Sharingan activated, and his innate talent is considerable. He'll learn quickly, and his proficiency with Shuriken and Kunai is excellent. As for Obito, being an Uchiha, he'll eventually awaken his Sharingan. At present, there's no skill with a higher payoff than Armament Haki for him.
Kakashi also has considerable innate talent and may learn quickly. Moreover, Kakashi's combat style could see significant improvement after mastering Armament Haki.
During the early stages when Chakra is insufficient, Haki doesn't need to be applied to Ninjutsu; reinforcing just the White Fang Short Blade would be sufficient, significantly enhancing attack capabilities.
"The Secret Jutsu I'm going to teach you is called Armament Haki," Mutsuki introduced.
Hearing this extremely unfamiliar name for a Secret Jutsu, Kakashi became even more convinced that this was a Secret Jutsu developed by Mutsuki himself.
"You should all know that besides the five basic Nature Transformations like Fire Release and Water Release, there's also a special Chakra Nature Transformation called Yin-Yang. Armament Haki belongs to the Yin Release category," Mutsuki explained.
Guy was starting to feel confused. The five major basic elemental natures felt like ancient texts to him, making him wonder how difficult this special Chakra Nature Transformation must be.
Shisui remained indifferent. He had already learned Yin Release, and his proficiency was decent. It wasn't solely due to his Sharingan; he had been studying Genjutsu with Mutsuki before.
"Wow, that sounds really impressive! The name even has 'Haki' in it!" Obito was quite eager to see the specific effects of this Ninjutsu.
Mutsuki concentrated Chakra in his right arm, and soon the entire arm rapidly turned black, resembling a pitch-black armor.
"Armament Haki can create a highly unique Chakra through Yin Release Nature Transformation, which can greatly enhance both defensive and offensive capabilities when attached to a person," Mutsuki continued explaining.
"Shisui, come and try stabbing my arm with a Kunai," Mutsuki prepared to demonstrate the actual effect of Armament Haki.
Shisui hesitated for a moment, but out of trust in Mutsuki, he took a Kunai from his pouch and approached Mutsuki. He swiftly stabbed at Mutsuki's arm, covered in the unknown black substance.
The other three disciples focused their attention on the Kunai and the arm about to be pierced.
Then, to everyone's surprise, the unexpected happened. The sharp Kunai left no trace on Mutsuki's shoulder, not even a scratch, as if it hadn't been attacked at all.
"Use all your strength," Mutsuki said.
Shisui nodded, gripping the Kunai tightly and thrusting it down fiercely. The previous experience had made him realize that Mutsuki's Secret Jutsu was no ordinary one, so Shisui felt reassured.
Clang!
A metallic clash resounded, and the tremendous recoil force from the Kunai made Shisui's hands tremble slightly.
Everyone could tell that Shisui had indeed exerted a great deal of strength this time.
However, when everyone's gaze returned to Mutsuki's arm, they found that it remained unchanged. The smooth, jet-black arm even reflected some sunlight.
"Use your Chakra and Total Concentration Breathing and continue," Mutsuki continued.
The use of Chakra by a ninja was a completely different matter.
"Got it," Shisui responded, quickly adjusting his breathing rhythm, entering the state of Flame Breathing, and concentrating his breath even further to attain the strongest power possible.
With the additional strength from his Breathing Technique, Shisui erupted with Chakra in his hands to further enhance his power, and then he thrust the Kunai with all his might towards Mutsuki's arm.
Bang!
After the Kunai pierced Mutsuki's arm, before anyone could see if Mutsuki's arm was injured, they witnessed the sharp tip of the Kunai directly breaking off and falling to the ground.
"His defense is too strong!" Obito exclaimed, staring at Mutsuki's arm, which remained unchanged, with wide eyes filled with disbelief. He felt that if this could cover the entire body, it would make battles incredibly safe, with no need to worry about injuries at all.
Guy understood why Mutsuki insisted on teaching him this Secret Jutsu.
If he mastered this Secret Jutsu, he wouldn't need to learn weapons anymore; he could simply use Armament Haki to confront others empty-handed.
Kakashi's eyes flickered. He remembered Mutsuki's initial words about simultaneously enhancing defense and attack. He was curious about the upcoming attack demonstration.
However, Mutsuki didn't end the demonstration of his defense there. He instructed the students to step back and then said to Shisui, "Use Phoenix Sage Flower Nail Crimson with all your strength to attack me."
If we talk about being impressed, it's definitely facing Ninjutsu head-on.
"Fire Release: Phoenix Sage Flower Nail Crimson!"
Because Mutsuki said to use full strength, Shisui didn't use the one-handed Kunai version. Instead, he completed the hand seals and then threw out a large number of Shuriken.
The rapidly advancing Shuriken touched the flames expelled by Shisui, instantly turning into dense clusters of small fireballs.
"To be able to use this level of Ninjutsu at this age!" Kakashi looked at the imposing Fire Release displayed by Shisui, feeling extremely surprised.
The first time he saw Shisui was at night while strolling with Obito and Rin. At that time, Obito mentioned that Shisui was a genius even greater than himself.
Initially, Kakashi didn't take Obito's words seriously, considering it was just Obito boasting.
However, after seeing Shisui's Fire Release, Kakashi couldn't say if Shisui could surpass him, but he was indeed a very strong genius.
Seeing the fireballs about to strike, Mutsuki immediately erupted with Chakra throughout his body, covering himself in Armament Haki, turning his entire body jet-black.
Boom!
The small fireballs continuously struck Mutsuki, triggering explosions that covered Mutsuki's figure completely in intense flames.
Obito strained to widen his eyes, hoping to see through the flames and catch a glimpse of Mutsuki inside. Unfortunately, without his Sharingan, all he could make out was a vague silhouette amidst the fire.
Mutsuki waved his hand as if swatting away mosquitoes. A powerful gust of wind instantly dispersed the explosion smoke, revealing his unscathed body.
"To be able to easily withstand Fire Release Ninjutsu head-on!" Kakashi, seeing that the black substance on Mutsuki's body remained unchanged, also revealed a surprised expression.
Kakashi already knew that Mutsuki could withstand this, after all, if Mutsuki couldn't handle it, why would he let Shisui go all out?
However, in Kakashi's assumption, Mutsuki's body should have undergone some changes, such as leaving traces on the black substance.
But in reality, Mutsuki's body showed no changes whatsoever. Even when Mutsuki dispelled the Armament Haki, it could be seen that his clothes remained undamaged.
It's worth noting that this was Fire Release, possessing both sharpness from the Shuriken and high temperatures from the flames. Kakashi felt that if this Ninjutsu hit an ordinary person, it could easily blow them up.
"Wow, that's so cool! This is the Ninjutsu I want to learn!" Obito looked at the Shuriken falling around Mutsuki and Mutsuki's unscathed appearance, instantly getting excited. In his mind, he began to fantasize.
He imagined himself and Rin on a mission, with Rin getting ambushed. He would activate Armament Haki to protect her from the attack and then ask her if she was hurt, all while remaining unscathed.
"I bet Rin-chan would be impressed by my coolness," Obito thought, picturing the admiration in Rin's eyes and couldn't help but grin foolishly.
"This is the defensive capability of Armament Haki. As long as your Haki is strong enough, you can even withstand Ninjutsu head-on," Mutsuki said with a smile.
"Of course, until you've mastered it to a certain extent, don't follow my example of using Color of Arms all over your body to resist Ninjutsu. I do it because my strength far exceeds yours," Mutsuki reminded them.
Using Color of Arms all over the body, except in special cases like Eight Inner Gates, is not recommended by Mutsuki under normal circumstances.
Focusing on one point is the ultimate development path for Color of Arms.
"You all come behind me, a little farther away. I'm going to unleash an attack," Mutsuki continued.
He expended Chakra to create Armament Haki, then began to concentrate the Armament Haki on his fist, preparing for a simple and straightforward straight punch.
All four disciples were completely focused on Mutsuki's fist, curious to see how powerful an attack enhanced with Armament Haki could be.
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