Only after dealing with matters in the Land of Waves and the Land of Water did Karn return, heading straight for Tsunade and Orochimaru's underground laboratory.
The moment Orochimaru saw Karn, his eyes lit up. "Mr. Karn, we've used up the serum. We've made some progress, but we need to move on to the next round of experiments."
After Orochimaru finished, Tsunade noticed Karn looking at her and picked up where Orochimaru had left off. "Orochimaru is right. We've collected a lot of useful data, and we can now be fairly certain that the Extremis virus can suppress the invasive growth of my grandfather's cells. His cells can also enhance the subjects' metabolic functions, allowing the two to approach a state of peaceful coexistence."
"What's the catch?" Karn asked.
"Just when we thought the experiment had succeeded, they exploded again. It might have something to do with their emotions."
Tsunade spoke helplessly. If the subjects had remained unconscious, they could essentially have declared their first experiment a success. The Extremis virus could rapidly heal any injury, even when they cut off a subject's hand.
But once a subject woke up, his emotions began to fluctuate. When they climbed to a peak, his body exploded violently.
Still, judging by the scale of the explosions, Tsunade and Orochimaru had indeed made considerable progress. After the last explosion, they had at least found a few intact bones.
"There should be equipment in the Shinobi World that can substitute for the data collection and medical testing devices. It's a little more expensive, but use that for now. As for the serum, I'll have it delivered in a few days. Let me take a closer look at the data first."
Karn rubbed his head as he spoke. Orochimaru had no qualms about experimenting on human lives. His methods were brutal and efficient, but they cost far too much money.
Karn had brought three sets of equipment, and the medical testing devices had already been completely destroyed. Compared with the cheap human lives, the cost of that equipment pained him far more. Besides, he didn't want to keep traveling between the two worlds just to deliver equipment to Orochimaru.
He might as well have several more sets custom-made in the Shinobi World. The testing equipment wasn't the core of the operation, anyway. If the other equipment were destroyed, that would truly hurt.
While Karn examined the experimental data from the past few days, Orochimaru spoke beside him. "If possible, it would be best to send over a wider variety of subjects: adolescents, women, children, and ninja."
Karn looked up at that. "Orochimaru, may I call you that?"
"Just call me Orochimaru."
"All right, then just call me Karn, too, Orochimaru. The first three are easy enough to arrange. The prisons in the Land of Fire have all of them. The last one might be difficult for me. Do you have any connections?"
Orochimaru smiled. "There are quite a few ninja held in Konoha's prison. But if we take people from there, they'll probably have a legitimate reason to interfere with what's happening here. I doubt that's a situation you'd want to see."
"I see. Then let me find a way."
Karn shook his head as he spoke. He would just spend a little more money and have Kakuzu capture some ninja. While he was at it, he could clear out the rogue ninja in the Land of Tea.
Tsunade didn't join this discussion. Although she had accepted human experimentation, she didn't want to actively participate in conversations like this. She probably clung to the thought that she had no other choice for her younger brother's sake. She could accept it passively, but she didn't want to take the initiative.
"You can even arrange for ninja? Impressive as ever, Karn."
Orochimaru smiled in praise. He was becoming increasingly interested in the organization behind Karn. Developing something like the Extremis virus would have been impossible without a professional team.
"It can even activate the Wood Release bloodline ability?"
Karn couldn't help asking in surprise when he saw that several subjects had displayed unusual traits.
"That's right," Tsunade replied. "As long as the Extremis virus doesn't go out of control, it can reproduce my grandfather's Wood Release ninjutsu."
If this experiment succeeded, Tsunade would want an injection herself. But she knew how money-grubbing Karn was. If he promised her one dose of serum, he wouldn't give her a single extra gram unless she could offer something tempting enough to move him.
For a while afterward, Karn traveled between the experimental base, Kawaki Town, and the Land of Fire's capital. By now, he was essentially the experimental base's logistics manager, arranging equipment and subjects. Sometimes he even returned to the Marvel Universe to bring Maya and Killian's research findings on the Extremis virus back to the Shinobi World.
Those two had never seen Hashirama cells, so Karn had no intention of giving them Orochimaru and Tsunade's research data. He would have no way to explain it.
Aside from that, Karn also set aside plenty of time to practice ninjutsu diligently. He had become fairly proficient with the Three Basic Techniques and the Shadow Clone Technique, though his hand seals were still a little slow. At his fastest, he could manage about three seals per second, but only when he performed exceptionally well. Usually, he could manage two per second.
His chakra affinities, however, had become rather strange. His chakra now possessed all five elemental affinities.
Even Kakuzu was astonished when he learned this, then shook his head and lamented that such excellent affinities were wasted on someone with Karn's aptitude. Neither his chakra reserves nor his talent for ninjutsu made him suited to being a ninja.
Karn suspected the change in his chakra affinities had something to do with Kakuzu's chakra. He wasn't originally from the Shinobi World and had never encountered chakra before. Strictly speaking, he was like the first group of people to whom the Sage of Six Paths had passed down chakra, only weaker.
Still, Karn didn't care much about his own strength. He had a very clear idea of his role. If he encountered danger he couldn't avoid, he would use the system to travel between the two worlds. That was already the equivalent of an invincible Flying Thunder God Technique, one that no barrier ninjutsu or sealing jutsu could restrict.
He learned other ninjutsu only to conceal his identity and movements. His research into the Extremis virus and Hashirama cells was likewise intended to strengthen his physique.
Karn saw himself as the boss, not a hired fighter charging into battle. He had paid Kakuzu thirty million ryo to teach him for a month just so he could learn the Earth Release: Hiding Like a Mole Technique, which would let him quickly slip underground and escape in an emergency in the Marvel Universe.
"Calm down, Tsuchiishi. If you survive, we'll let you leave and give you some money, provided you cooperate-"
"Aaaah!!"
Bang!
Before Orochimaru could finish, the subject in the experimental isolation area exploded again. This time, however, only one arm exploded, and it was slowly regenerating. Bone, blood vessels, chakra pathways, and the rest were visibly growing back.
"Did it work?"
At the sight, Tsunade quickly recorded all of the subject's physical reactions and pulled up the ratio of Hashirama cells to Extremis virus.
"Heh heh. It seems my hypothesis was correct, Tsunade."
Orochimaru smiled smugly. Although his experiments had killed many subjects, those subjects had not gone to waste. The man before him was ample proof of that. All that stood between him and success was more repeated testing.
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