The pool of concentrated natural energy—capable of dissolving and consuming anything in the world—lay directly beneath Shihouin Naraku's suspended form.
The Slug Sage's powerful Senjutsu chakra completely enveloped Naraku's body, ensuring that no part of him remained exposed to the deadly waters below.
Given the terrifying corrosive speed demonstrated by the pool, Naraku couldn't guarantee that even the elemental transformation of his Mera-mera no Mi Devil Fruit abilities would provide protection.
Besides, if he truly wanted to succeed in this final stage of training, he had to personally endure the erosion of natural energy without any external protection.
Using either elemental transformation or Armament Haki to shield himself would certainly prevent success in achieving true immortality.
"Try making contact first," the Slug Sage instructed gently.
Following her guidance, Naraku cautiously extended his left hand toward the shimmering pool surface.
The moment his fingertips made contact, the rippling water instantly engulfed his entire left hand, corroding his palm and fingers into ash within seconds before they completely vanished.
"Incredible!" Naraku gasped through gritted teeth.
Excruciating pain shot through his entire nervous system as he instinctively yanked his arm back, but it was already too late. Everything below his left wrist had disappeared into nothingness.
Under the stimulation of his Senjutsu chakra, Naraku's regenerative abilities had reached extraordinary levels. His missing hand began regrowing at a speed visible to the naked eye, the new flesh and bone appearing completely identical to the original.
Clenching and unclenching his newly restored fist, Naraku contemplated what had just occurred.
"I see now. The practice of Sage Mode truly is progressive by nature. If someone skips the second stage of training and attempts to jump directly to this final stage, it becomes nearly impossible to compensate for the incomplete physical preparation."
"Even though the pool water corrodes my body, I can recover to my original state with the help of Senjutsu chakra, which provides the maximum possible safety margin for this training."
"In that case, let's continue," Naraku declared to the Slug Sage.
The ancient being nodded approvingly, then used her chakra to carefully wrap Naraku once more and slowly lower him into the deadly waters.
The majestic yet gentle Senjutsu chakra formed an incredibly thin protective barrier around Naraku's body, creating a buffer against the pervasive corrosive power of the concentrated natural energy.
Without the Slug Sage's assistance, the risk of Naraku's training would increase exponentially if he came into direct contact with the pool water unprotected.
"Be extremely careful, little Naraku," the Slug Sage warned.
Having descended to the bottom of the pool, Naraku settled into a cross-legged meditation position within the protective membrane. Upon hearing the Slug Sage's reminder, he began rapidly condensing the chakra within his body.
The protective barrier then began to grow unusually transparent—a clear sign that its thickness was being deliberately reduced.
BOOM!
Terrifying pressure assaulted him from every direction, threatening to crush Naraku's body into powder.
The pool water, formed from pure concentrated natural energy, began seeping through the thinning protective membrane that surrounded him.
The Senjutsu chakra within Shihouin Naraku's body immediately destabilized and collapsed. The carefully maintained balance between his physical energy, spiritual energy, and natural energy began to deteriorate into chaos.
The agony of corrosion intensified dramatically as the exposed surfaces of Naraku's skin began developing severe burns and scarring. Even with his enhanced recovery abilities powered by Senjutsu chakra, his healing couldn't keep pace with the relentless erosion caused by the natural energy.
The two forces engaged in a desperate struggle within his body. Either the overwhelming natural energy would completely destroy Naraku, or he would successfully adapt to this concentrated natural energy and manage to condense new Senjutsu chakra under these extreme conditions.
As the Senjutsu chakra in his body rapidly diminished until it disappeared entirely, the external natural energy began gaining the upper hand. Extensive corrosion scars began appearing across Naraku's entire body.
At this critical juncture, he could rely only on his innate regenerative abilities to battle against the natural energy that formed the pool's deadly waters.
However, the situation showed no signs of improvement—in fact, it continued to worsen steadily.
Naraku could distinctly feel a powerful suction force emanating from the pool water itself, attempting to pull him completely free from the protective barrier created by the Slug Sage and devour him entirely.
"No! That's enough!"
At the critical moment when Naraku's consciousness began to fade, the Slug Sage immediately extracted him from the pool, bringing him back to the safety of the cave floor.
Water splashed dramatically as Naraku collapsed onto solid ground, his chest heaving as he struggled to catch his breath.
"How do you feel?" the Slug Sage inquired, her gentle voice carrying a hint of concerned amusement.
"Honestly? That was rather embarrassing," Naraku admitted with a rueful smile.
He raised his arms to examine the extensive scarring covering his body, noting how the marks were already beginning to fade slowly.
Without the oppressive influence of the pool water, his regenerative abilities once again gained dominance, and his healing rate was steadily accelerating.
"So while submerged in the pool, I must simultaneously repair my body damage, maintain chakra balance, and find a way to condense new Senjutsu chakra during the complete disruption of natural energy flow."
"Exactly correct," the Slug Sage confirmed.
"This is truly demanding! Without that protective barrier, I would have dissolved completely the moment I entered the pool."
The Slug Sage observed as Naraku's injuries continued healing and returning to normal before asking, "Well then, do you wish to continue?"
"During this particular stage of training, progress can only be made gradually and patiently. If you sense that something is seriously wrong with your physical condition, there's absolutely no need to force yourself to continue."
Naraku shook his head firmly. "I'm fine. I can still endure this level of training for now. Although I didn't have enough time to properly recover while submerged in the pool, as long as I can exit the water, my regenerative abilities ensure that I'll be perfectly fine."
"Very well then. Let's continue," the Slug Sage agreed.
The thin protective membrane once again surrounded Naraku's form, slowly lowering him back into the pool water.
The familiar sensations of tearing flesh and acidic erosion returned immediately, and dense networks of scars quickly covered every inch of Naraku's exposed skin.
After several minutes had passed, the Slug Sage determined that Naraku had reached his current limit and carefully extracted him from the water.
"Again!" Naraku declared as soon as he caught his breath.
"Again!"
"Again!"
This pattern continued repeatedly throughout the day.
As Naraku entered and exited the pool countless times, the duration he could withstand submersion gradually increased. Although the improvements were relatively small each time, they represented genuine progress nonetheless.
According to the Slug Sage's explanation, this final stage of training required an enormous investment of time and patience.
Naraku had mentally prepared himself for this reality.
Achieving true immortality was never meant to be simple or easy. Finding the training difficult was completely natural and expected.
Over the following days, Naraku dedicated virtually every waking moment to this intense practice, taking only the minimal rest necessary to maintain his health and mental clarity.
The results of such dedicated training proved extremely gratifying.
"Little Naraku has performed admirably," the Slug Sage commented with genuine admiration. "You are the very first ninja to progress this far in the training!"
Naraku dried his upper body with a towel while expressing his dissatisfaction with the current pace. "While that may be true, I still feel that my progress remains somewhat slow. Although the time I can remain at the bottom of the pool has increased noticeably, I still cannot break free from the protective barrier and move independently within the water."
"The primary issue is that the pool water's corrosive properties are simply too overwhelming. I cannot properly condense my chakra while submerged. If I rely purely on physical strength and endurance to fight against the natural energy, I remain at a severe disadvantage."
"Despite having such powerful regenerative abilities, the limitations imposed by the concentrated natural energy prevent me from utilizing my healing to its full potential."
The Slug Sage responded gently, "If your injuries were caused by conventional damage from weapons, jutsu, or other typical sources, with little Naraku's current recovery speed, such wounds might heal completely within the blink of an eye."
"However, the injuries you sustain are caused specifically by the erosion of pure natural energy. Recovery from this type of damage will always be extremely difficult and time-consuming."
"Actually, even if you were to fail at this particular stage of training, as long as you manage to preserve your life, little Naraku's current level of mastery would still be remarkable. Even without achieving true immortality, significantly extending your natural lifespan would be quite achievable."
The Slug Sage's meaning was perfectly clear. If Naraku chose to abandon this final stage of training, it wouldn't represent a significant problem. He had already successfully mastered Sage Mode, and his overall strength had improved dramatically, which fulfilled his original training objectives.
Unless he possessed an absolutely burning desire to achieve genuine immortality, there was no compelling reason to continue investing time and effort in such an extremely dangerous practice.
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