With one expansion after another, the main body of the Research Institute had grown from the original underground Kara base into a complex covering a radius of over a dozen kilometers.
In addition to hundreds of researchers, the facility housed a large number of volunteers and a massive population of prisoners. Combined with the supporting logistics staff and various guards, the entire Research Institute was home to over ten thousand people.
Laboratories, warehouses, prison cells, dormitories, testing grounds, living quarters, and isolation zones—all of these together made the Research Institute look more like a vibrant city than a secret Akatsuki base.
In truth, the existence of the Research Institute was no secret in the shinobi world. Leaving aside the large-scale transport of prisoners, the sheer volume of equipment, experimental materials, and daily supplies being shipped there could not be hidden from view.
Therefore, whether it was the major Hidden Villages or the forces hiding in the dark of the Black Market, everyone knew about this giant Akatsuki facility. However, out of fear of "A's" overwhelming power, everyone turned a blind eye and pretended not to know. This was also why many shinobi from various villages were able to find the Institute and volunteer for experiments.
Deep in the mountains, roughly forty kilometers from the main district of the Institute, lay a heavily guarded fortress. Only a handful of people in the Institute knew of this secret location, and it maintained almost no contact with the outside world.
Late at night.
Amidst a series of rapid whistling sounds, several figures landed steadily in front of this mountain fortress. Looking at the quiet structure before her, Delta stood with her hands on her hips and asked bluntly, "Hey, is this the place?"
Ranmaru, following behind her, nodded. "Yeah, this should be it."
Delta curled her lip. "To suddenly call us here for a shift change in the middle of the night... the higher-ups really treat us like servants."
Ranmaru replied, "This fortress isn't marked on the Institute's maps. It seems to be a classified outpost."
Delta didn't waste any more words. "Let's go. Let's see what's inside."
Ranmaru and several test subjects who had undergone cell transplantation followed her into the fortress. These subjects were "defective" products; although they had survived the surgery, they had failed to obtain any of Otsutsuki Shibai's "Shinjutsu." Having lost their research value, they were recruited as temporary guards under the command of Delta and Ranmaru.
Despite being "defects," these people had still obtained the power of the Otsutsuki. Even the weakest among them had the strength of a Jonin, and the stronger ones could rival Kage-level powerhouses. Though few in number, they were a force to be reckoned with.
Inside the fortress, Delta and Ranmaru met Yakumo, who was responsible for guarding the site. Seeing "D," Delta's lip twitched slightly. She had challenged Yakumo privately several times, and every match had ended in her crushing defeat. Facing Yakumo, she had no choice but to suppress her temper.
Seeing that Delta had no intention of speaking, Ranmaru stepped forward. "Arriving as per Command Center instructions to provide support. Here are our transfer orders."
Yakumo took the orders, checked them, and nodded. "The orders are correct."
While Yakumo was checking the papers, Ranmaru scanned the interior of the fortress. From the inside, the quiet facility appeared even more grand, as if the entire heart of the mountain had been hollowed out. Every entrance and corridor was quietly guarded by figures in black robes—judging by their attire, these were Tenseigan puppets.
"So many guards..." Ranmaru was secretly alarmed.
Not only was the fortress hidden and secluded, but the internal security was incredibly tight. To have a figure like Akatsuki's "D" personally stationed here was so serious it was impossible not to be curious.
The others in the group also sensed the fortress's abnormality. These defective test subjects were all former prisoners. Having survived the surgery and gained massive power, they all harbored thoughts of escaping the Institute, but had stayed their hands only because they knew the main facility's security was airtight.
Now that they were away from the main district, they began to scheme. Seeing how hidden this fortress was, they felt it must contain some sort of treasure, and greed began to take root. Of course, under the eyes of Yakumo, Delta, and Ranmaru, they didn't dare show their thoughts.
Ranmaru asked, "Where is our defensive sector?"
Roar—
Just as Yakumo was about to answer, a low, guttural animal roar echoed through the fortress. The sound seemed to penetrate through layers of stone; though not loud, it struck directly at the heart, causing an instinctive wave of palpitations.
Delta and Ranmaru both looked toward the depths of the fortress, toward the source of the roar. While others might not know, they knew exactly what the source was. Their hearts tightened: "So, this is where the Ten-Tails is being kept!"
Yakumo's expression remained unchanged. She instructed, "The exterior is guarded. Your squad is responsible for the interior. This is the structural map; the red zone is your sector."
"Understood," Delta and Ranmaru nodded.
Shortly after, Delta and Ranmaru's squad took over the interior security. Looking at the massive cage embedded deep into the mountain, Delta whispered to Ranmaru, "We're probably thinking of the same thing, aren't we?"
Ranmaru nodded silently.
"The higher-ups actually let us guard this place... heh, they're certainly bold," Delta said, glancing at the squad members scattered about.
The defective subjects were huddled in groups of two or three, whispering to one another. When Delta's gaze swept over them, they looked away guiltily.
Ranmaru was worried. "While the thing in that cage isn't something they can touch, we have to make sure they don't do something stupid and drag us down."
Delta nodded slightly.
At that moment, one of the squad members cried out, "Who's there!?"
Before the words had even faded, a pained wail echoed through the fortress. Everyone spun around to find a figure had appeared out of nowhere. Dressed in the red-cloud cloak of the "Dark Akatsuki" and wearing a swirl mask, the intruder stood like a ghost behind one of the squad members.
The wail had come from that member; half of his body had just been shredded by a distorting vortex!
"Enemy attack!"
In an instant, everyone, including Delta and Ranmaru, went on high alert.