"Ordinary ninjutsu uses the energy within your body—that is, combining your physical energy and spiritual energy to create chakra, which then becomes the power source of your techniques."
"But Sage Arts are different. On top of that foundation, they draw in and control a third type of energy—one that exists in the natural world, permeating all things. This is what we call natural energy."
"When these three energies are combined, they form a special kind of chakra—the Sage Chakra we mentioned before. Any technique or skill that uses this Sage Chakra is what we call Senjutsu."
"Doing so allows your ninjutsu, genjutsu, and even taijutsu to increase in power drastically…"
Senju Mori sat cross-legged on the ground, quietly listening to the explanation about Sage Arts. The one speaking was a colossal slug—ten times larger than a Tailed Beast, its body stretching for several hundred meters.
This spectacle could only be seen within this secret realm. Even Hashirama Senju, whose chakra reserves surpassed all others in the history of the shinobi world, could not summon the true body of the Slug Sage into the outside world.
In fact, across all shinobi history, perhaps only the Sage of Six Paths—who once served as the Jinchuriki of the Ten-Tails—possessed enough power to do something like that.
After resolving everything in Uzushiogakure and returning to Konoha, Senju Mori immediately began his training in Sage Mode.
Since his research on Hashirama Cells would take time to progress, learning Sage Mode and mastering Senjutsu was, for now, the most efficient way to strengthen himself.
Using the reverse summoning technique performed by the Slug Sage, Senju Mori soon arrived at one of the three unexplored sage regions—the unique natural sanctuary known as Shikkotsu Forest.
The air here was so thick with moisture it felt like it could drip; every breath carried the scent of ancient life mixed with a faint acidic tang.
Wherever he looked, enormous skeletal remains lay scattered—bones of beasts so large they seemed impossible. Mori had no idea what creatures they once were. Perhaps ancient giants drawn by the overwhelming natural energy here.
After death, their bones remained like pale mountain ranges, forming the very structure of this hidden world.
Pools of steaming, heated liquid lay between them, forming countless waterfalls of various sizes due to the altitude differences—creating the only ambient sound in this otherwise silent realm.
The scenery looked beautiful, almost otherworldly—yet it contained deadly danger.
The waterfalls and pools did not contain ordinary water, but a pale yellow acid filled with dense natural energy.
Any creature falling into it would dissolve into white bones in moments.
Occasionally, bubbles rose from the depths, bursting with a light corrosive mist.
In the distance lay what seemed like a vibrant forest.
Unlike the white bone plains and yellow acid pools, it seemed full of life and vitality.
But in truth, it was made of unique fungi native only to this realm. They glowed with green luminescence, sinking slightly and rippling softly when stepped on.
And at the center of all this stood the impossible form of the Slug Sage.
Its massive body rested quietly on the ground. The eyes at the ends of its two antennae gazed downward, while its blue-and-white patterned body pulsed rhythmically—like the heartbeat of the entire land.
Its very presence felt like part of the earth itself, radiating vast, ocean-like Sage Chakra that overflowed with warmth. Mori felt the insignificance of his own existence in its presence.
"Lord Mori, now please use the mucus I secrete to sense and begin absorbing the natural energy around you."
Among the Three Big Unexplored 'Sage' Regions, Shikkotsu Forest was perhaps the most polite and gentle in its teaching style.
The Slug Sage spoke with great courtesy, its voice serene and ethereal—almost soothing.
Although he had long known about this enormous slug, and knew that it had the habit of addressing its contractors as "Lord,"
when such a mountain-sized creature actually appeared before him, speaking in a gentle voice completely at odds with its size and calling him "Lord Mori,"
Senju Mori couldn't help feeling a strong sense of dissonance.
The Slug Sage was a truly unique lifeform in the entire shinobi world. It was born even before Ōtsutsuki Kaguya descended upon the earth and had already lived for more than a thousand years.
It was no exaggeration to say that its existence was even older than the ancestors of the Senju clan.
At this moment, Senju Mori sat bare-chested, with a small slug—only the size of his palm—slowly crawling across his body. Its cool and soft body continuously secreted a transparent mucus.
Mori quietly closed his eyes, fully focusing on sensing the natural energy that permeated the surrounding air.
At first, his perception was filled only with darkness and the flow of his own chakra.
But with the help of that mystical mucus, the world's "true form" gradually unfolded before his "eyes"—countless tiny, life-like motes floating in the air. These were the omnipresent particles of natural energy.
The ground beneath him, the acidic pools and fungi around him, and even the entire space within Shikkotsu Forest all emitted vast, steady pulses of life—like a gigantic living creature breathing in silence.
Shikkotsu Forest was already a special sanctuary rich in natural energy, but with the aid of the slug's mucus, a unique sensation welled up in him. Mori felt as if countless "currents" of air were surging toward his body.
As these "currents" flowed into him, strange markings began spreading rapidly across his face, his eyes bulged slightly, and his skin faintly started becoming translucent…
Just as training in Mount Myōboku's Sage Arts led to toad-like traits, and Ryūchi Cave's Sage Arts caused snake-like features to appear,
absorbing natural energy through Shikkotsu Forest caused Mori's body to shift toward a slug-like form.
However, the abnormal changes soon receded.
The Slug Sage's ethereal voice echoed again, filled with a calming warmth.
"Excessive absorption of natural energy can cause the body to mutate, gradually stiffen, and eventually become part of Shikkotsu Forest."
"But please rest assured. My clone will ensure your safety and absorb the surplus natural energy as needed."
"Next, please try to guide the natural energy entering your body and mix it with your spiritual and physical energies in a precise ratio of 1:1:1 to maintain balance and produce Sage Chakra…"