Natural energy surged wildly inside Orochimaru's body, raw and unrefined.
He forced every ounce of his will into suppressing it. His pale, almost bloodless face flushed unnaturally, muscles twitching, features twisted. Sweat beaded along his brow as he trembled under the strain.
Improper use of natural energy was lethal.
From Mount Myōboku, it meant petrification into a frog statue. From Ryūchi Cave, it meant madness, rampage, grotesque mutation, then death.
Those who drew energy directly from the White Snake Sage risked transformation into serpents if their minds collapsed. Jūgo and those branded with Cursed Seals mutated in their own ways, their bodies warped into violent forms.
For nearly ten minutes, Orochimaru battled the storm within him. At last, his body steadied. His breathing slowed. He opened his eyes, lips curling.
"After so many years, one has finally succeeded."
The White Snake Sage regarded him. "Good. Now I will explain the method of practicing Sage Mode here in Ryūchi Cave. I will only explain once... so listen well."
Her words spilled like a lesson carved into stone.
To awaken Sage Mode, one must first possess Senjutsu Chakra. But having Senjutsu Chakra did not mean one could wield Sage Mode.
Ordinary chakra was born by balancing physical and spiritual energy. Senjutsu Chakra required adding natural energy to that balance, weaving it perfectly into the whole.
Each of the three energies, body, mind, and nature, had to remain equal, one-third each. Perfect integration birthed true Senjutsu Chakra.
Fall short, and mutation followed.
Sometimes minor.
Sometimes catastrophic.
Sage Mode itself was like a valve. Open it, and natural energy flooded in, creating Senjutsu Chakra. Close it, and the danger receded. Control of the 'switch' was everything.
But natural energy was treacherous, slippery as a snake.
A single mistake could kill.
Even the Toad Sages of Mount Myōboku did not hold maximum Senjutsu Chakra at all times. They maintained only a fraction within their bodies, drawing in more when battle demanded. Humans had an even harder time.
Jūgo's clan was the opposite. Their Sage Transformation lacked a 'valve.' They lived in constant symbiosis with nature, absorbing energy involuntarily.
When emotions spiked or when the air grew too rich with energy they lose control, and be consumed by berserk transformations.
Orochimaru's Cursed Seal was his attempt to fix that flaw. He built a valve into Sage Transformation itself. The seal stored and released Senjutsu Chakra like a controlled floodgate.
It was brutally effective. But brutally dangerous.
The Cursed Seal's power rivaled Sage Mode in raw scale, but it ripped apart those unworthy to contain it. Those who adapted survived with their sanity intact; those who failed, perished.
Orochimaru's genius was undeniable. His invention could not be dismissed.
Sage Mode had both a high floor and a high ceiling.
In the legends, Hashirama Senju showed its pinnacle. Jiraiya embodied its lower limits.
Naruto's later Six Paths Sage Mode was something else entirely, a gift, not a technique, transcending what mortals could learn.
The Cursed Seal's scale was different; its ceiling rivaled titans, but its floor was abysmal. At its peak, Sasuke's Susanoo fused with the Cursed Seal created a monstrosity whose potential might surpass even Hashirama. At its weakest, Orochimaru's test subjects during Sasuke's training were pitiable wrecks, barely human, shattered by the seal's weight.
For ordinary shinobi, the Cursed Seal was more attainable than Sage Mode. More universal. More practical. But it could never match Sage Mode's clean amplification of jutsu.
Sage Mode could boost ninjutsu, taijutsu, and genjutsu by several-fold or sometimes dozens of times. Cursed Seals risked their user's life to scrape the same results.
Even Sage Mode had limits.
The greater the amplification, the greater the drain on one's own body and chakra. Hashirama could endure such terrifying consumption because of his constitution.
Almost no one else could.
Thus, in practice, Sage Mode's boosts hovered between a few times to over tenfold, depending on mastery, chakra quality, and stamina.
Beyond sheer power, natural energy granted other gifts such as heightened senses, hardened bodies, and unique traits depending on the region.
Naruto could fall from the sky and walk away unharmed, his durability superhuman.
Kabuto's body regenerated endlessly, his vitality monstrous.
Hashirama's regeneration might not even have come from Shikkotsu Forest but from his innate Sage Body and Yang Release nature.
The differences lay in the environment and the creatures who had perfected their own Senjutsu. Mount Myōboku's techniques fit toads. Ryūchi Cave's fit snakes. Shikkotsu Forest, slugs.
Humans borrowed what they could manage.
White Snake Sage finished her explanation at last. "You know the path. Now find rooms in the temple. Practice. Survive. That will prove your worth."
Orochimaru bowed low. Beside him, Uchiha Gen did the same.
They chose separate rooms, close enough to rush to each other in crisis, far enough not to interfere.
Orochimaru, already infused with natural energy, began immediately to shape Senjutsu Chakra.
Gen, however, had to start at step one; absorbing nature itself.
Even outside Ryūchi Cave, his keen senses could detect natural energy. Here, it was overwhelming.
He had held back before, too cautious to risk it. Knowledge alone wasn't enough. You didn't build an atomic bomb just because you'd read about it.
But with Ryūchi Cave's accumulated wisdom, with techniques refined over millennia, he felt ready.
Seated cross-legged, Gen let the energy flow into him. It glowed faintly in the dim chamber, threads of life itself sinking into his body. His soul's power, sharpened perception, and Sharingan control locked down the wild current.
When the natural energy matched his internal chakra, he began fusion.
Not recklessly but a sliver first.
If he failed, he could smother the backlash with his control. And as insurance, his Mangekyō spun open. If disaster struck, Izanagi would erase it.
One chance each day, that was his ace. A safety net that no ordinary shinobi could dream of.
Uchiha ancestors had forged Izanagi as a weapon against fate. Gen was using it as training wheels. Luxurious didn't begin to describe it.
With such a crutch, even dullards could brute-force Senjutsu eventually. Gen, armed with a soul strengthened by the Soul-Soul Fruit and a body it had nourished, was no dullard.
He was exceptional.
Carefully, strength and subtlety blended. The first fusion succeeded. A wisp of Senjutsu Chakra sparked into being.
The second attempt was bolder, one-fifth of his chakra which also succeeded.
Confidence surged; too much of it even.
He poured the rest in at once.
The backlash hit like a collapsing mountain. His control shattered. Energy raged, threatening to tear him apart.
Watching unseen, the White Snake Sage shook her head. "Impatient child. Tonight, my attendants will feast."
But then Izanagi rewrote reality. The deadly failure never happened.
Her eyes narrowed. "Oh?"
Recognition flashed. The Uchiha's forbidden jutsu. Izanagi. But his eyes remained intact, no blindness, no toll. Could it be his Mangekyō itself wielded Izanagi as a personal ability?
A boy this afraid of death was dangerous indeed. With such a power, his odds of mastering Sage Mode and even forging a human-exclusive version skyrocketed.
Meanwhile, Gen exhaled heavily.
Lesson learned. No shortcuts.
He returned to steady increments, one-fifth at a time, patiently molding chakra until all of it became Senjutsu.
Nine days blurred past. His world shrank to a rhythm; eat, rest, and practice. Then exchange insights with Orochimaru, or Seek White Snake Sage's guidance. Finally, absorb natural energy, refine it, fail, then refine it again.
Unlike Jiraiya or Naruto's harsh toad cuisine, Gen had prepared proper food before coming. He wasn't about to starve while training to godhood.
Piece by piece, everything aligned; Ryūchi Cave's knowledge, Orochimaru's aid, White Snake Sage's insights, and his own unique qualities.
On the tenth day, he sat in stillness, ready to claim what he had built.
Senjutsu Chakra surged through his body, tracing circuits like living rivers. It converged at his brow.
A wave of power burst outward, shaking the cavern. Serpents writhed and fled.
All of Ryūchi Cave turned its eyes toward his chamber.
White Snake Sage, her three retainers, and Orochimaru rushed forward, unable to ignore it.
Within, the change revealed itself.
A purple vertical mark split open on Gen's brow, jagged like a lightning bolt or an eye. Gold ripples spread across the whites of his eyes. Behind his head, a halo shimmered with seven colors; black, gold, green, blue, red, yellow, and white.
From the sky fell golden petals, and from the ground bloomed golden lotuses.
Sacred chants rang out as if the air itself was singing.
On the bed, Uchiha Gen sat like a deity.
A sage reborn.