After a moment of silence, Diarmuid looked at Orochimaru and asked, "So, this jutsu has a hidden ceiling – physical compatibility? The soul cannot exceed a certain threshold, or it triggers an unpredictable chain reaction?"
"Most likely," Orochimaru nodded. "Dan Kato was a man of immense talent and genius, once considered the last glory of the Kato Clan. It was his death that caused the clan to lose all faith in the shinobi profession and transition into other fields. I suspect that Dan, having practiced the Spirit Transformation Jutsu since childhood, likely reached the limit of his body's compatibility. It made him powerful enough, so he probably stopped further training after that."
Diarmuid nodded, remaining silent as he pondered the issue.
The soul and the body...
It seemed natural that they would influence each other. Just as with Orochimaru's Living Corpse Reincarnation, changing bodies causes the soul to weaken accordingly because they aren't a perfect match. There was a clear precedent for this. Even when the soul of Orochimaru's hands was severed, his physical arms withered in response.
They thought about it for a long while, but neither Diarmuid nor Orochimaru could reach a definitive conclusion.
Examples of soul weakening were easy to find, but power resulting from a soul being too strong and causing physical issues was something Diarmuid hadn't encountered in either world. He couldn't judge if the outcome would be good or bad, but if the Kato Clan chose to stop practicing at a certain point, there might be a dangerous risk involved.
"Sigh..." Diarmuid exhaled. "As expected, there is no perfect jutsu in this world."
"That is only natural," Orochimaru said with a light laugh.
After a short pause, he added, "However, I feel you are worrying needlessly. For the time being, this isn't a problem for you to solve, but for me. Your physical constitution is far too powerful, well beyond the scope of a normal human. Theoretically, the limit of your body-soul compatibility should far exceed that of an ordinary person. You could practice for decades and still might not hit the ceiling."
"Maybe not decades. The Spirit Transformation Jutsu involves the conversion of physical energy. In my view, this includes, but is not limited to, Chakra. I believe that once Natural Energy is integrated and balanced within the body, it can produce similar effects, working with the Spirit Transformation Jutsu to strengthen the soul. Given my reserves of Chakra and physical energy, once I master the basics, my progress will likely be explosive. I might hit the limit in ten years or so," Diarmuid noted.
Orochimaru considered this. The descriptions in the scroll supported that theory. Although they hadn't officially started the training, Diarmuid's inherent advantages meant he would indeed move much faster than a normal person. What took others a year might take him only two or three months.
"In any case, there's no need to worry yet. I'll try it first to see what it looks like to reach the limit, and what happens if one tries to break through it," Orochimaru said with a predatory smile.
This was the epitome of a pioneering scientific spirit.
Orochimaru wasn't just someone who used others as research subjects; in his eyes, all living things were equal, anyone could be a subject if it benefited his research, including himself. This was evident from his past: he hadn't hesitated to inject himself with Diarmuid's serum cells, he was the first to undergo the Living Corpse Reincarnation after its development, and now, he was volunteering again.
"You are my most important strategic research partner; nothing can happen to you. Don't be so reckless..." Diarmuid tried to persuade him.
"Rest assured. Through my various modifications, my Chakra and physical energy already far exceed the average person's. My training speed should be fast, but my ceiling isn't as high as yours. I'll likely reach the limit before you do. If push comes to shove, I can switch to a weaker body to artificially lower the compatibility ceiling, accelerating the process so I can see what happens during a breakthrough," Orochimaru explained.
He wasn't wrong. Although Orochimaru came from a civilian background without innate high-tier physical stats, he was a man of science. If he wasn't born with it, he researched it. Between his Soft Physique Modification, Cursed Seals, and other experiments, he had outfitted himself with countless upgrades. Despite the numerous battles he had fought, he was rarely seen actually running out of Chakra.
Heaven only knows how much he had modified himself or what extra "hardware" he had installed.
His progress with the Spirit Transformation Jutsu wouldn't be slow. And as he said, if he needed to, he could just hop into a "scrub" vessel via Living Corpse Reincarnation to lower his ceiling and test the results.
Before Diarmuid could speak, Orochimaru continued: "Moreover, even if the body suffers an accident, I can simply bypass it by switching vessels again. If it truly comes down to it, I can switch bodies multiple times to forcibly weaken any overflowing soul power and return to normal. There is no real risk for me in this experiment, so don't worry."
Diarmuid thought it over and realized Orochimaru was right. Someone who can swap bodies at will and doesn't care about the consequences... can truly do whatever they want.
Perhaps the Spirit Transformation Jutsu wasn't as flawless as they first hoped, but Diarmuid realized he was overthinking it. He had originally sought the jutsu specifically for matters involving the Sharingan, to boost his spiritual energy in preparation for awakening it later. Whether it had a ceiling was a secondary concern. If it did, would he really just not learn it?
"I suppose I was worrying about nothing. I always want the absolute best, the most powerful..." Diarmuid laughed.
"It is human nature to pursue such things. There is nothing wrong with it," Orochimaru said calmly.
Diarmuid smiled. "Do you know what I admire and like most about you?"
Orochimaru gave him a curious look, took a sip of his tea, and pondered for a moment. "My talent?"
"Wrong." Diarmuid shook his head. "Your talent was what attracted me initially, but what I like is how you can always find a perfect reason to convince me that I haven't done anything wrong. Hahahaha!"
Orochimaru paused, then laughed as well. "And do you know what I like and admire most about you?"
"What?" Diarmuid asked, genuinely interested.
"You possess immense power, yet you haven't lost your humanity because of it," Orochimaru said.
Diarmuid was taken aback. If someone else said that, it would sound like a typical "hero" line. Coming from Orochimaru, it sounded strange.
However, Diarmuid soon waved it off and said sentimentally, "There's nothing wrong with pursuing power. But viewing power as everything, elevating oneself above the world and calling oneself a 'God,' is actually quite boring and meaningless. I once knew a friend who possessed unparalleled power and ruled the world for centuries..."
"Otsutsuki Kaguya?" Orochimaru recalled a story Diarmuid had mentioned and instinctively asked.
"No, I don't know Kaguya. I'm talking about someone from my world," Diarmuid smiled.
"And then?" Orochimaru asked, intrigued.
"And then... then she must have been very lonely. She probably felt the whole world had become dull. So, she went to another world. Perhaps she's starting an interesting new life over there," Diarmuid mused.
Orochimaru really wanted to retort: Is your world that weird? Can people just go to other worlds whenever they want?
Thinking of this, a flicker of curiosity stirred in Orochimaru's heart. For a man who pursued infinite unknowns and mysteries, how could he not be interested in a new world?
"So, do you have a way to go to other worlds now?" Orochimaru asked.
"What? You're interested?" Diarmuid laughed.
Orochimaru nodded seriously. "To be precise, I am extremely interested!"
Diarmuid chuckled. "Not currently. I don't really understand how it works myself. My arrival here was somewhat passive. I used to carry a massive amount of space-time energy and presence. When that energy became large enough, it naturally activated a certain factor in me and brought me to this world."
He paused before continuing. "But since arriving here, I haven't activated any space-time presence. So, I'm not sure what the situation is. Whether I can go back or travel to a new world is a total unknown..."
"Space-time?" Orochimaru murmured. "Perhaps it's because you haven't learned any space-time ninjutsu? If you learn some, you might activate that mysterious trait of yours."
Diarmuid was stunned. "Probably not? I already know space-time ninjutsu. Aren't the Substitution Jutsu and Summoning Jutsu technically space-time techniques?"
Orochimaru looked at Diarmuid with disdain. "Those are the lowest-level applications of space-time. Practically every ninja knows them. Please do not lump those in with true space-time ninjutsu. Real space-time techniques are incredibly powerful..."
"You mean the Flying Raijin? The jutsu developed by the Second Hokage, Senju Tobirama?" Diarmuid recalled.
"The Flying Raijin is one, but there are others. Kumogakure has the Heavenly Transfer Jutsu, which is also powerful. Each has its own strengths," Orochimaru explained.
"Maybe I can try to learn those later. I've always been interested in the Flying Raijin," Diarmuid said.
"Didn't you make a deal with that Black Zetsu? When the time comes to stir up trouble in Konohagakure... that will be your chance," Orochimaru reminded him.
"Exactly. That's what I was thinking," Diarmuid agreed.
The Flying Raijin was documented within the Scroll of Seals, and Orochimaru had personally guaranteed it.
Of course, it was a notoriously difficult jutsu to master. One had to have a high affinity for space-time to even learn it. Senju Tobirama was a genius, but after his death, the Flying Raijin was lost to the world for a long time. Konoha spent massive resources but couldn't find a successor until Namikaze Minato appeared. After Minato died, the jutsu was lost again, only his three guards together could barely perform a crude version of it.
It was clearly an insanely difficult technique.
But Diarmuid figured that since he had literally crossed worlds, his space-time affinity should be top-tier. He believed he could master the Flying Raijin.
As Diarmuid and Orochimaru chatted about everything from the Spirit Transformation Jutsu to trivial matters, Nohara Rin cautiously knocked on the door. She peeked her head through a crack and said, "Diarmuid-sama, Orochimaru-sama, it's time to eat."
"Oh, coming, coming!" Diarmuid replied with a smile. He finished his tea in one gulp and stood up.