Orochimaru listened to Diarmuid's teasing and shot him a glance. After scanning the surroundings to ensure they were alone, he nodded. "It seems you have indeed discovered the weaknesses and flaws of the Living Corpse Reincarnation."
Diarmuid nodded in return. "Come, let's talk at my place."
"Very well." Orochimaru did not refuse. He agreed immediately and followed behind Diarmuid.
The two of them soon arrived at Diarmuid's room.
Only then did Orochimaru speak. "I didn't expect your perception to be keen to such an extent."
"I just happen to care deeply about everyone's health," Diarmuid quipped with a smile.
"That's a bit terrifying," Orochimaru grumbled before continuing. "Even I only realized on the third day that there was a minor issue with my soul."
"As I thought," Diarmuid replied. He poured hot water into a teapot and looked at Orochimaru. "What kind of tea would you like?"
"Anything is fine; I'm not picky," Orochimaru said casually.
Diarmuid took out some high-quality tea leaves "confiscated" from Hanzo of the Salamander from under the table and began brewing.
He then spoke up. "It seems my intuition was correct. Your soul strength has indeed weakened, but it doesn't seem to be missing anything?"
"Naturally, it isn't missing. A missing soul would be a catastrophic problem," Orochimaru stated without hesitation.
A weakened soul and a missing soul were two entirely different matters.
A weakened soul was relatively easy to resolve; the simplest method was rest, and it would recover naturally over time. Originally, if his Living Corpse Reincarnation didn't have the restriction of needing a new vessel every three years, his soul wouldn't suffer from continuous, deepening weakness. With enough time, he could recover through rest.
However, a missing soul was a treacherous problem. By comparison, a weakened soul was like catching a cold, you just need rest to get better. A missing soul, on the other hand, was like a physical disability. For a normal person, a severed hand or leg won't grow back.
The most direct example of this occurred in the original story when the Third Hokage, Sarutobi Hiruzen, used the Reaper Death Seal. The Reaper's blade sliced away the soul of Orochimaru's hands, sealing them inside the Reaper's stomach along with Hiruzen.
That was a classic case of a missing soul. Orochimaru suffered immensely because of it; his combat power and his various research projects almost completely collapsed. He tried countless methods but couldn't heal his hands. Ultimately, he only returned to normal after retrieving the missing soul fragments from the Reaper's stomach.
Precisely because he frequently used the Living Corpse Reincarnation, his soul became chronically weak. When Hiruzen took his hands, his soul became incomplete, causing his spiritual energy to hit an extreme low. Consequently, when he tried to seize Sasuke's body, the tables were turned. His soul and spiritual energy were no match for "Sasuke" and his Sharingan. Not only did the reincarnation fail, but he ended up giving everything he had to Sasuke for free.
"Is that so? That's good then." Diarmuid smiled and asked, "Do you have a way to solve this yourself?"
Orochimaru shook his head, though he didn't seem overly concerned. "This doesn't affect me much. My soul is just slightly weakened, and my spiritual energy has dipped a bit. A year or so of normal rest should resolve it."
Diarmuid was slightly surprised. "It can recover completely on its own in just a year or so?"
"Of course," Orochimaru nodded.
"Are you sure?" Diarmuid asked again, curious.
"Please do not question my professional expertise regarding my own body," Orochimaru said, sounding quite annoyed.
"Hahaha, my apologies," Diarmuid laughed it off, but he already had an inkling of the answer.
Orochimaru's spiritual energy and soul strength would inevitably fall into a cycle of weakening after the Living Corpse Reincarnation, a continuous process that usually got worse over time.
But since that wasn't happening yet, one could conclude that either Orochimaru had miscalculated (which was unlikely), or... perhaps the soul weakness increases with the number of times the Living Corpse Reincarnation is performed?
Or maybe, because this first reincarnation was from his original "factory" body, the loss was relatively small. In the future, since he wouldn't be using "original parts," the soul depletion from the Living Corpse Reincarnation might exceed the recovery period of three years. This would leave Orochimaru in a state where he could never fully recover before needing the next vessel, causing him to become progressively weaker...
It wasn't until he used a White Zetsu as a vessel, which offered nearly perfect compatibility, that he avoided this downward spiral. Was that why he could still act so flamboyantly in the Boruto era?
Diarmuid felt this was a strong possibility.
He then said, "Perhaps it can heal in a year or so, but first, that year of weakness will indeed have a negative impact on you. Secondly, this is only your first Living Corpse Reincarnation. You'll surely perform it many more times. I doubt even you can guarantee that your future state will always remain as manageable as it is now."
As Diarmuid finished, Orochimaru's expression turned solemn. After a moment of reflection, he had to admit that Diarmuid was right; such a scenario was very possible.
In fact, the risk of it worsening was high. He realized that this reincarnation was unique because he had started from his original body. From now on, there would be no more "original factory" source.
Thinking of this, Orochimaru looked up at Diarmuid. "You are right."
"Hahaha! That's why this Spirit Transformation Jutsu is so important for you. While recovering naturally, you should study this secret technique. It can strengthen the soul and spiritual energy through training. Once you master it, you might recover to your peak in just three to five months. If you keep practicing, by the time your next reincarnation comes around, your soul strength will likely be high enough that even with some loss, you won't fall into a weakened state again," Diarmuid said with a grin.
With that, he tossed the Spirit Transformation Jutsu scroll to Orochimaru. "Take a look. I think it's excellent. The power of this technique might even exceed my imagination, because it seems to have no upper limit!?"
…
The Spirit Transformation Jutsu was indeed a technique that could enhance one's soul strength and allow for the free manipulation of the soul's movements.
The reason Diarmuid said it was useful to Orochimaru wasn't just for soul recovery; the second reason was the method of soul manipulation itself.
The so-called Spirit Transformation Jutsu involved controlling one's own soul to forcibly enter the enemy's soul. By using the power of one's own soul, the user could seize control of the enemy's body or even directly annihilate the opponent's soul.
From this perspective, the Spirit Transformation Jutsu must inherently strengthen the user's soul. Otherwise, if you enter someone else's body to fight for control on their home turf without sufficient soul strength, wouldn't you just be delivering your own head on a silver platter?
Manipulating one's soul to seize control of another's body struck Diarmuid as being fundamentally similar to Orochimaru's Living Corpse Reincarnation.
Sure enough, after a brief look, Orochimaru acted as if he had found a treasure. "The Kato Clan's Spirit Transformation Jutsu truly exceeds my expectations. It seems my previous assessment of Dan's strength was slightly off. He was stronger than I imagined... just a bit unlucky."
Orochimaru was right. Dan Kato was indeed formidable. After all, someone who could attract Tsunade could never be weak, especially someone who confidently aimed to become Hokage.
However, his strength wasn't well-rounded. His true power lay entirely within this Spirit Transformation Jutsu.
His soul was so powerful that he could forcibly break free from the Reanimation Jutsu before it was dispelled, traveling across vast distances just to see Tsunade one last time. That spoke volumes of his power.
But... his physical body clearly didn't match his soul's level, leading to his unfortunate death on the battlefield.
Diarmuid didn't respond to Orochimaru's comment. Instead, he placed the tea on the table, picked up a cup for himself, and leaned back on the sofa to sip.
He waited for Orochimaru to finish reading.
A long time later, Orochimaru looked up, still wanting more. He closed the scroll and said, "...It seems to be exactly as you said. This technique... really has no upper limit?"
"Right? It seems that as long as you follow the steps and keep practicing, your soul will continue to grow stronger!" Diarmuid said excitedly.
Orochimaru nodded, but then had a moment of realization. "No, there is an upper limit. That limit is likely a person's lifespan. Because life is finite, truly infinite training doesn't exist. However..."
At this point, he looked at Diarmuid, then at himself, and then thought about the current members of the Yorozuya. It seemed only that unlucky kid, Juzo, was still bound by the shackles of a natural lifespan.
Neither he nor Diarmuid, nor Kakuzu or Sasori, had the "natural death" option on the table. At most, they could be killed in battle.
From that perspective, weren't they all perfect candidates for practicing the Spirit Transformation Jutsu?
Though, he wasn't sure if the physical conditions of Sasori and Kakuzu would allow for it. Kakuzu was possible, but for Sasori... what exactly was the deal with that Core of Living Flesh? Orochimaru wasn't certain.
"But that problem isn't a problem for us, hahaha!" Diarmuid laughed loudly.
In the hands of a normal person, the Spirit Transformation Jutsu might not seem vital. But in the hands of people like them, a technique that could infinitely strengthen the soul was simply overpowered!
Orochimaru nodded happily, but soon frowned again. "Wait, something isn't right."
"What's wrong?" Diarmuid blinked and asked quickly.
"I once talked with Dan Kato about these things and discussed aspects of the Spirit Transformation Jutsu. It seems that once the soul reaches a certain level of strength, it is no longer advisable to continue practicing... Otherwise..." Orochimaru's brow furrowed.
"Otherwise what?" Diarmuid pressed.
"Let me think... I don't remember clearly, but... it seemed like there would be a reactive effect on the physical body? The soul and the body are complementary... or something along those lines," Orochimaru explained.
Although he himself was a master of soul research, having improved the Reanimation Jutsu and developed the Living Corpse Reincarnation, those were mostly techniques for manipulating souls. Regarding the fundamental nature of the soul, Orochimaru clearly wasn't as experienced as an old hand like Dan Kato, who had spent years rooted in that specific field.
Even if Dan Kato didn't "research" the soul per se, practice makes perfect. Moreover, this was a technique passed down through the Kato Clan for generations; there were bound to be other secrets.
"The soul's influence acts upon the self?" Diarmuid was stunned for a moment. He suddenly remembered how, in the original story, after Orochimaru's hands were taken by Hiruzen, his physical arms underwent a change, becoming withered and decayed.
That was a negative effect caused by a missing soul. But... what if the soul became too powerful, exceeding the capacity of the physical body?