"This Shinno really is a genius."
Nagi frowned as he studied the Zero-Tails. The creature's characteristics were different from the ultimate summoning beast's; it was much closer to a true Tailed Beast. It could be sealed within a human body, and it wouldn't die from lack of food or water. The ultimate summoning beast, on the other hand, would have simply expired after a long enough time without sustenance. Nagi had even tried to see if he could fuse the two beasts, but it was a no-go. Their attributes were too different.
The energy of negative emotions... Does an Edo Tensei summon, with its infinite chakra, count? A flash of inspiration struck Nagi. He didn't know how a bug as powerful as infinite chakra for a reanimated corpse had appeared in this world—it defied all scientific explanation, yet it was an undeniable, unreasonable fact. Since the world had such a massive loophole, Nagi couldn't be blamed for exploiting it.
He dragged the dying Shinno over to a jutsu formula, then took out a test tube containing Asuma's blood. Without wasting the body, he used it to reincarnate Asuma.
"I... how did I get here? Where is this?" the newly awakened Asuma asked, his mind still in a daze before he could even take in his surroundings.
But Nagi didn't answer him, nor did he give him time to think. There was no point in torturing Asuma; torturing the Third Hokage would be much more interesting. He plunged a kunai with a suppression tag into the back of Asuma's head. Asuma immediately became an immortal puppet, completely under the caster's control. Nagi then moved him into the Sky Fortress, into the sealing chamber where the Zero-Tails was held, and let the beast devour his chakra.
"Holy shit, it actually works!" Nagi's jaw dropped. Asuma's chakra was being continuously devoured by the Zero-Tails. And every time it was depleted, for some reason, Asuma's body would regenerate, and his chakra would be restored. Infinite mana...
"Hahahaha! I'm a goddamn genius!" Nagi threw his head back and laughed.
He had originally thought that while a Tailed Beast's chakra was easy to come by, the vast negative emotions of a human were not. He had thought there was no hope for the Zero-Tails to evolve into its complete form. Who would have thought that feeding it the chakra of a reanimated ninja would actually work? Nagi had experimented before, extracting some chakra from an Edo Tensei summon for research. He had discovered that the chakra of the dead could not be used by the living, even though it seemed essentially the same as normal chakra. When absorbed into a living person's body, it would cause extreme discomfort, even illness and death.
So, Nagi surmised that the chakra of an Edo Tensei body was a form of negative, deathly energy, which was why it could be used by the Zero-Tails. The Zero-Tails was special; besides Tailed Beast chakra, it also absorbed the negative emotions of the living for its own use. And the chakra of the dead was likely rich in negative energy.
At the same time, Nagi frowned. The Zero-Tails' chakra, filled with negative energy, was completely different from that of the nine Tailed Beasts. If they were positive, then the Zero-Tails was negative. The young girl Amaru's constitution was truly one in a million, rarer than that of the Uzumaki or Senju clans, to be able to be compatible with the Zero-Tails and its immense negative emotions. But whether to make Amaru a jinchuriki was a matter for later. He would wait until she was a little older and see how things went. For now, Kimimaro was enough for his village's second generation of combat power. It was a pity Suigetsu had been captured by Orochimaru; otherwise, he would have gone and gotten him too. And he didn't know where Zabuza had picked up Haku. But Nagi had also found a few orphans with good potential in the Land of Iron, whom he could slowly cultivate.
After finishing his experiment with the Zero-Tails, Nagi took the pitiful Asuma next door to the ultimate summoning beast and fed him to it.
The ultimate summoning beast was starving. Having been locked up for so many years, it had long since gone mad with hunger. Although its brain was already a chaotic mess without any intelligence, the instinct of hunger made it even more frenzied. Seeing Nagi throw a person in, it immediately shot out its tentacles, grabbed Asuma, and began to gnaw...
In the next second, the half-eaten body of Asuma began to rapidly regenerate. The ultimate summoning beast took another bite.
[SKRAWW!]
The beast roared at Nagi, its eyes seemingly questioning him: What is this disgusting thing? It then angrily stomped Asuma's half-eaten body into a pulp. It was mad with hunger; it wanted to eat meat, a living creature with flesh and blood, not this thing that tasted like dirt.
BOOM!
BOOM!
It continuously slammed against the sealing jutsu's bars, trying to break out, but it was all in vain.
From its red, frenzied compound eyes, Nagi read its meaning.
"You're so big, and you have such a big appetite. Who the hell can afford to feed you? Eat it or don't," Nagi chuckled, about to take Asuma away.
But then, something unexpected happened. The ultimate summoning beast, seemingly unable to bear its hunger any longer, opened its mouth wide and swallowed Asuma whole as Nagi was about to take him away.
What would happen if a reanimated person was swallowed whole and couldn't get out? Before, when it had bitten off half of him, the remaining half of his body outside had naturally started to regenerate. Now that all of Asuma had been swallowed, he would naturally regenerate inside the ultimate summoning beast's stomach.
Nagi rested his chin on his hands, pondering the question. Asuma's body, inside the beast's stomach, was digested, then regenerated, then half-digested again, then regenerated again. In this continuous process of regeneration, Nagi noticed that the ultimate summoning beast was also slowly evolving, changing its own body structure, adapting, and beginning to absorb a small amount of Asuma's death-attribute chakra.
Slap!
Nagi slapped himself on the forehead. He had forgotten he had another test subject. With a flash of the Flying Thunder God, he brought over a White Zetsu. Having had all its marrow extracted, the Zetsu was already on the verge of death. Nagi placed it on the ground and used the Edo Tensei, turning it into Shinno.
"Ah... I... Uchiha Nagi? Is this the Edo Tensei? You killed me?" The moment Shinno regained consciousness, he noticed something was different. He was a knowledgeable man; although his strength was inferior to Orochimaru's, his knowledge of strange and unusual things was not.
Nagi didn't waste any words with him. He picked up a kunai with a suppression tag, intending to plunge it into Shinno's head and erase his consciousness. To make a person watch their own body be eaten again and again... he had already died once, to make him die hundreds more times was too cruel. Nagi's hatred for Shinno wasn't that deep. So, he only planned to erase his consciousness before feeding him to the ultimate summoning beast.
"Wait, wait! We can talk about this! I know a way to solve the side effects of the Living Corpse Reincarnation, to allow you to achieve true immortality! Are you interested?" Shinno knew that once his consciousness was erased by the Edo Tensei, he wouldn't be able to speak anymore.
"What are you trying to say?" Nagi asked.
"The Living Corpse Reincarnation... Orochimaru got it from me. You know that, right?" Shinno asked cautiously, a sense of relief washing over him. Death, it seemed, was not a big deal to him.
"Of course I know. By taking over another person's body and devouring their soul, you replace them and obtain their body. But don't tell me you don't know about the side effects," Nagi said with a smile.
"I know... there's a way to do it without any side effects." Shinno knew this was his only chance to survive. "Use cloning. Clone your own body and use it as a vessel for the Living Corpse Reincarnation. That way, there are no side effects at all."
Nagi: "...!?"
Well now. You scientists have really taken the ninja world's dirty tricks to a whole new level.
But Nagi wasn't so easily convinced. "If there were no side effects, then why has Orochimaru never cloned his own body to use as a vessel for his reincarnation? Don't tell me he's stupider than you and didn't think of that."
Shinno smiled confidently. "Using a clone of your own body as a vessel... of course there are no spiritual side effects, because it's your own body. But there are some minor physical side effects."
"I call it... the 'womb's bewilderment'."
Nagi said flatly, "Stop beating around the bush. If what you say is true, I can consider letting you go and letting you use the Living Corpse Reincarnation to clone a body for yourself."
As for how to resurrect after death, Orochimaru had experience with that. He had even exploited the Shinigami's bug several times. Sasuke had used a part of his cells and the soul fragment from Anko's curse mark to revive Orochimaru. And after being revived, Orochimaru was not an Edo Tensei body, but a body of flesh and blood. If the former could be explained away, the latter was a true exploit of the system. Orochimaru had put on the Shinigami mask, summoned the Shinigami—a jutsu that required the sacrifice of one's own soul—and then Orochimaru had simply used the Edo Tensei to possess a White Zetsu's body. The Shinigami had then... crashed? It couldn't find Orochimaru's soul to reap? So, for Shinno to use an Edo Tensei body to possess a cloned body to revive himself... Nagi wasn't surprised. The Shinigami of this world was more like a computer system, a non-sentient entity. As long as you could find its bugs, you could avoid its reaping and revive yourself.
"The reason I call it the 'womb's bewilderment' is because a cloned body lacks the ten months of gestation in a human mother's womb. So, the potential of a clone is limited. Moreover, it takes at least eighteen years for a human to grow from birth to adulthood. But who has the patience to wait eighteen years for their clone to mature? So, growth accelerators are used to speed up the clone's development from infancy to adulthood, ensuring it grows into an adult in a matter of months. Tell me, how can a body that has been hastily forced to grow be as healthy as a normal person's?"