Kakashi looked at the scene with a thoughtful expression.
From the beginning, he felt it strange. Shisui addressing Mokgetsu as Teacher Mokgetsu wasn't odd because Mokgetsu is a teacher at the Ninja Academy, but having two of Mokgetsu's shadow clones here was very strange.
Cultivating within the village shouldn't require sending two shadow clones to scout the way in advance, as training locations are usually pre-decided, not determined impulsively.
Seeing Mokgetsu skillfully instructing Nohara Rin, coupled with Nohara Rin's performance, Kakashi's doubts were resolved.
Shisui and Nohara Rin were likely additional disciples taken in by Mokgetsu, which is why Mokgetsu brought them along for training.
Kakashi even had a conjecture that perhaps Obito and Might Guy had also long become Mokgetsu's disciples, hence their rapid increase in strength.
After all, they're all from the Ninja Academy. Perhaps Mokgetsu found them pleasing to the eye and decided to teach them.
"Shisui, set aside your cultivation for now. Today, I want to teach a secret technique." Mokgetsu interrupted Shisui's training.
With his Sharingan already activated, Shisui was inherently gifted in learning anything related to the yin release and haki.
The originally continuing Shisui ceased his training immediately and headed over to where Mokgetsu's true form was.
For now, Mokgetsu wasn't planning to teach Nohara Rin haki, as her current training regimen was sufficient to keep her occupied for a long time, including Mystical Palm Jutsu, Monster Strength Power, and Chakra Scalpel. Once she progressed enough in those, she could then learn haki.
Since learning haki now wouldn't benefit her with her limited chakra, Nohara Rin was the disciple with the least chakra amount within Mokgetsu's pupils, currently only having seven hundred.
The limited chakra has multiple reasons. Firstly, her natural chakra amount was quite low, far below that of Might Guy and Obito when Mokgetsu first checked. Additionally, Nohara Rin joined as a disciple a semester later than Obito and the others and didn't have a breathing technique suited for her.
The reason for teaching others was that Might Guy would see qualitative improvements after learning it, and since he learned slowly, the earlier he started, the sooner he would grasp it.
Shisui already had his Sharingan activated and was naturally talented, so he'd learn quickly. Moreover, he was very proficient with shurikens and kunai. Obito, being an Uchiha, was bound to activate his Sharingan eventually, and currently, no skill seemed to offer greater benefits than Armament Aura.
Kakashi, too, was naturally gifted and could potentially learn quickly, and mastering Armament Aura would significantly enhance his combat style.
During the earlier stages when chakra was insufficient, one could forego using haki to enhance ninjutsu, and merely enhancing the White Fang Short Blade would suffice, significantly boosting attack capabilities.
"The secret technique I want to teach you is called Armament Aura." Mokgetsu introduced.
Hearing the unfamiliar name of this secret technique, Kakashi was even more certain that it was something developed by Mokgetsu himself.
"You must all know that besides the five major basic elements like Fire Release and Water Release, there are special chakra nature changes known as yin and yang, to which Armament Aura belongs within the yin release."
Might Guy was already bewildered, as even the five basic elements seemed like a heavenly script to him, let alone special chakra nature changes.
Shisui remained calm, having already mastered the yin release with commendable proficiency, not entirely owing to his Sharingan, as he had previously studied genjutsu under Mokgetsu.
"Wow, it sounds really powerful. The name alone is imposing!" Obito eagerly anticipated the specific effects of this ninjutsu.
Mokgetsu concentrated chakra on his right arm, and soon the entire arm turned black, looking as if it was clad in pitch-black armor.
"Armament Aura can be created through yin release nature transformation into a very special chakra, which can be attached to a person's body to greatly enhance defense and attack capabilities," Mokgetsu continued explaining.
"Shisui, use a kunai to stab my arm and see." Mokgetsu prepared to demonstrate Armament Aura's actual effect.
A hint of hesitation flickered in Shisui's eyes, but due to his trust in Mokgetsu, he fetched a kunai from his ninja pouch, approached Mokgetsu, and quickly stabbed towards Mokgetsu's arm enveloped in an unknown black substance.
The other three disciples focused their attention on the kunai and the arm about to be struck.
Then, to everyone's surprise, the sharp kunai didn't leave a single mark on Mokgetsu's shoulder, not even a white blemish, as if it hadn't been attacked at all.
"Use all your strength." Mokgetsu instructed.
Shisui nodded, gripping the kunai firmly with both hands and stabbing down forcefully. The previous attempt had made him realize Mokgetsu's secret technique wasn't simple, so Shisui was now at ease.
Bam!
A metallic clashing sound resounded, and the tremendous rebound force from the kunai made Shisui's hand slightly tremble.
Everyone could tell Shisui had indeed used significant force this time.
When everyone's gaze returned to Mokgetsu's arm, they discovered that it still showed no change. Under the sun's rays, the smooth, black arm even seemed somewhat reflective.
"Continue using chakra and Full Concentration Breathing." Mokgetsu further instructed.
Whether ninjas use chakra makes a world of difference.
"Okay." Shisui quickly adjusted his breathing, entering the Breath of Flame state and concentrating his breathing further to harness the maximum strength.
With the breathing technique's strength augmenting him, Shisui erupted with hand chakra to further boost his power, and finally, he attacked Mokgetsu's arm with full strength.