Meanwhile...
Three hundred meters beneath Kirigakure lay an enormous natural cavern that had been completely hollowed out.
Nothing remained of its original geological structure. In its place stood cold, smooth metal walls and humming reishi power conduits.
Along with densely packed rows of cylindrical cultivation tanks.
The tanks held all kinds of twisted biological tissue, some resembling Hollows whose fusion had failed.
Others resembled ninja remains grafted with Cursed Seals, slowly rising and sinking in eerie green nutrient fluid.
The air reeked of formalin mixed with blood.
At the center of the cavern was a circular testing ground over fifty meters in diameter.
Layers upon layers of sealing inscriptions covered the floor, and twelve metal pillars carved with talismans stood in a ring.
Thick reiatsu chains extended from the tops of the pillars, their other ends-
Binding the enormous, turtle-like Isobu tight.
His mountain-sized body was pinned firmly to the ground, his three python-like tails hanging limp.
Thick, dark purple fluid seeped from the gaps in his shell.
His savage head hung low, his single eye shut. Only his chest still rose and fell faintly.
Orochimaru stood at the console on the edge of the testing ground, wearing a spotless white lab coat. His golden, serpentine eyes gleamed with fervor in the dim light.
He held a metal syringe as thick as an arm, its barrel filled with viscous black liquid that churned and bubbled constantly.
It was a derivative of the Hōgyoku Fragment-the "Hollowfication Serum."
"Injection trial number one thousand three hundred and twenty-seven, begin." Orochimaru licked his lips, his voice trembling slightly with excitement.
"Increase the dosage to one hundred and twenty percent of the previous trial. Target the seventh nerve ganglion cluster beneath the shell."
He pressed a button on the console.
A mechanical arm descended from