Hoshiyomi thought for a moment before asking:
"So—have you figured out any good way to learn Ryūchi Cave's senjutsu?"
Hearing the question, Orochimaru shook his head, looking somewhat dejected:
"This really is a very peculiar type of energy. It's completely different from the chakra system we humans use, yet at the same time it bears some similarities.
After three days of research, all I've managed to do is confirm some of senjutsu's properties through experimentation.
According to the White Snake Sage, senjutsu is essentially the control of natural energy. This energy is normally difficult for humans to perceive; one needs guidance from these Sages to even have a chance of detecting it.
Once a human successfully absorbs natural energy, if they can manage to perfectly balance it with chakra in a 1:1 ratio, they can greatly enhance the power of ninjutsu, genjutsu, and taijutsu—and even unleash techniques beyond human imagination.
The White Snake Sage wasn't lying. Senjutsu—or rather, natural energy—as a type of energy not naturally absorbable by the human body, is extremely dangerous."
As he spoke, Orochimaru led Hoshiyomi over to a lab table. From a drawer beneath, he pulled out a row of transparent vials. Picking one up, he explained:
"This is a solution containing natural energy, created after I removed the toxins from the White Snake Sage's venom."
Orochimaru then grabbed a white mouse from a cage behind him:
"This is a specially bred mouse, containing trace amounts of chakra in its body."
He injected the solution into the mouse. At once, the mouse began thrashing violently. Through his perception, Hoshiyomi could clearly sense the little creature struggling desperately with its pitiful reserves of chakra against the invasive, unknown energy.
Under the watchful eyes of Hoshiyomi and Orochimaru, the mouse resisted at first, then began undergoing drastic changes.
Its four limbs began to shrink, while its tail grew longer. The white fur on its body started to shed, replaced by scales.
In its new half-snake, half-mouse form, it became noticeably more aggressive and violent. The quiet rustling noises it made before turned into a loud, frantic banging against the cage's walls until its head was bruised and bloody.
Seeing it had completely transformed into a monster, Orochimaru flicked his sleeve, sending out two snakes that quickly swallowed the mutated mouse whole.
"The White Snake Sage wasn't lying," Orochimaru said flatly. "If I recklessly injected myself with natural energy as it demanded, I'd likely end up just like that."
Watching the mouse's transformation, Hoshiyomi couldn't help but swallow hard. Such a result… it seemed even more severe than the consequences of Mount Myōboku's senjuts
Looking at the scene before him, Hoshiyomi quietly dismissed certain thoughts he had been harboring.
Frowning, he said to Orochimaru:
"Since you already know how difficult Ryūchi Cave's senjutsu is, why not give it up? Why not learn Mount Myōboku's senjutsu like Jiraiya did?"
At that, Orochimaru's brow furrowed.
"I could never do that. First, because I refuse to admit defeat. Second, Ryūchi Cave and Mount Myōboku have been mortal enemies for a thousand years. As Ryūchi Cave's contract holder, there is no way I could ever learn Mount Myōboku's senjutsu."
Hearing this, Hoshiyomi slapped his forehead. He'd forgotten about that detail.
Orochimaru, seeing Hoshiyomi's expression, gave a faint smile and said:
"Actually, it's not that there's no way at all. I don't believe I'm completely without hope of learning senjutsu.
The White Snake Sage of Ryūchi Cave said I couldn't learn senjutsu only because he thought my body couldn't withstand the natural energy required for it.
But I believe the body can be modified. Just like my snake-like body and Soft Physique Modification, human potential is limitless. I firmly believe that through genetic modification, I can alter my body bit by bit, gradually adapting it to natural energy."
Hearing this, Hoshiyomi immediately thought of the Cursed Seal from the original story. Orochimaru's current line of thought lined up almost exactly with his future experiments.
The only thing missing between the two was Jūgo. If they brought Jūgo back for research together, then Orochimaru's present idea might very well become the prototype for the Cursed Seal.
And in fact, Orochimaru had succeeded—the Cursed Seal wasn't perfect, but it did indeed produce effects similar to senjutsu. It could be considered a degraded, incomplete form of senjutsu.
...
Leaving Orochimaru's lab, Hoshiyomi fell into deep thought on his way back.
When it came to senjutsu, Hoshiyomi actually knew even more than Orochimaru. Having read the original story, he knew well how crucial senjutsu was. In his plans, senjutsu was an ability he absolutely had to master.
Because when it came time to face the Ōtsutsuki clan in the future, unless he wielded their own powers, the only alternative would be to rely on natural energy.
But Hoshiyomi had neither a Sage's body nor Sage's eyes, and he wasn't related to the Sage of Six Paths. Using the Ōtsutsuki bloodline's powers was basically out of the question. If he only depended on cell transplantation, the best he could hope for was to turn into some half-baked mutant like Kabuto after his modifications.
Therefore, if he wanted to play a decisive role in the Fourth Great Ninja War, learning senjutsu was absolutely essential.
Senjutsu was the only power system in the Naruto world capable of rivaling Six Paths–level strength. Senjutsu—or rather, natural energy—was the true foundation of this world. Only by using the world's primordial force could one possibly contend against the abilities of the progenitor of chakra.
According to the manga, this world originally had no chakra. It wasn't until the Divine Tree appeared, and Ōtsutsuki Kaguya harvested and consumed the chakra fruit, that this world first gave birth to chakra.
From Hoshiyomi's perspective, the so-called Divine Tree was nothing more than a converter—an instrument that extracted natural energy and transformed it into chakra.
This setting was reminiscent of a certain alien race in Dragon Ball, who also planted trees to absorb a planet's life force, bearing fruit that, once eaten, would make their people stronger.
This was also why the Great Toad Sage had worked so hard to convince the Sage of Six Paths—because Kaguya's plan had always been short-sighted, sacrificing the future for immediate gain.
Kaguya only wanted to use natural energy to create chakra and an army of White Zetsu to oppose other Ōtsutsuki. But she never considered that once natural energy was fully drained, the entire world would wither and collapse.
Even if she managed to defeat Kinshiki and Momoshiki, it would be meaningless—before long, the shinobi world would become a dead planet thanks to the Divine Tree. Both her rule and her White Zetsu army would crumble without a fight.
And meanwhile, every other species in this world would perish alongside them.