Chapter 266: A Powerful Secret Technique

Steel rang through the underground training hall.

"Not enough."

Orochimaru spat a blade from his mouth and turned Sasuke's kusanagi aside. The exchange ended with cold steel resting against the younger shinobi's throat.

"Your actions must not become predictable. Feint. The more possibilities you consider, the greater your chance of surviving."

Sasuke had grown taller and harder during his time beneath the earth. Little remained of the boy who first entered the base, but his expression held no gratitude.

The hall around them bore evidence of previous sessions. Sword cuts scored the walls at shoulder height, craters marked failed substitutions, and blackened stone showed where Sasuke's lightning had chased Orochimaru through the corridor. None of it had produced a clean victory.

He absorbed every lesson anyway.

"Again."

His strength still fell short. Even with the Cursed Seal active, Orochimaru's experience and unnatural body overwhelmed him.

The sannin withdrew his sword and laughed.

Sasuke attacked before the laughter ended. Lightning coated his blade and turned the next clash blue-white. Orochimaru let the current pass through a shed layer of skin, emerged from his own mouth several paces away, and tapped the back of Sasuke's neck with two fingers. Another death in a real battle.

"Good. Do not disappoint me. Otherwise, killing Itachi and avenging the Uchiha will remain beyond you."

"I will kill him with my own hands."

"You are far from ready. Combat experience is only one problem. Your Sharingan remains underdeveloped beside your brother's. In another year and a half, I expect a body worthy of its potential."

Sasuke's fists tightened. He trusted the Sharingan, yet opponents like Tonbo and Orochimaru repeatedly showed him that his eyes still lacked something.

"I promised to raise you beyond Itachi," Orochimaru continued. "Unlike the Third Hokage, I do not worship conventional limits. I will use every method available until—"

"Until my body becomes yours," Sasuke finished. "If you can take it, I do not care which of us kills Itachi."

Orochimaru's tongue passed across his lips.

"Come with me."

He turned toward a side passage.

"We are still training."

"I would enjoy continuing, but Kabuto found something inside you. If we ignore it, Konoha may stand at the entrance tomorrow."

Sasuke frowned and followed.

The possibility offended him because he had inspected himself repeatedly after leaving. He had searched clothes, weapons, and seals for trackers. He never imagined that a foreign structure might hide among nerves so small even the Sharingan overlooked them without knowing where to focus.

Who in Konoha had touched him without his knowledge? Kakashi? Naruto? Someone in the hospital? For a moment he considered Itachi and the secrets beneath the Uchiha compound. Perhaps his brother had marked him to return when the Sharingan reached the required power.

Orochimaru sounded amused rather than alarmed.

"An exceptionally brilliant young man created this. Had the Third Hokage's Will of Fire not chained him to Konoha, I would have liked to cooperate with him."

The comment narrowed Sasuke's suspicion without answering it.

They passed through a deep tunnel and stopped before a heavy door. Kabuto waited in the laboratory beyond it, gently shaking a test tube.

Several more tubes rested in a rack behind him. Some contained tiny fragments that had grown into branching webs; others held failed cultures that had collapsed into gray sediment. Notes covered the table with measurements of chakra intake, response to living tissue, and the distances at which activity changed.

A branching strand moved in the liquid like a root beneath dark water.

"Lord Orochimaru," Kabuto said. "The latest culture is stable."

"Any new discoveries?"

Sasuke stared at the tube. The specimen had been removed from his body.

His Sharingan opened to three tomoe. Chakra circulated inside the branching structure, and the strand absorbed energy from the surrounding solution to sustain itself.

"What is it?"

"Human nerve tissue," Kabuto answered. "A powerful Yin Release transformation has refined and extended it. The nerve can move through living bodies and ordinary matter, drawing physical energy, mental energy, or chakra from the host to maintain itself. Someone separated it from a larger network and implanted it inside you through a secret technique."

Kabuto had tried starving one culture. When deprived of chakra, it consumed the trace physical and mental energy suspended in the growth medium. When placed against metal, wood, and stone marked with chakra, its tips explored the new material as though searching for more information. It behaved less like severed tissue than an extension awaiting a distant command.

Sasuke's expression darkened.

He had carried another person's nerves for more than a year. Orochimaru's examinations had only now exposed them. If the hidden structure answered its creator, then Sasuke's location—and perhaps his life—had never been fully his own.

"What else?" Orochimaru asked.

Kabuto adjusted his glasses.

"I cultivated and divided the extracted sample for testing. Your first suspicion was correct. Combined with the appropriate technique, the implanted nerve can connect to the target's body, disrupt the nervous system, and take control of movement."

One chart showed a small animal whose leg moved after Kabuto stimulated the embedded fragment. The nerve did not merely shock muscle. It entered the host's existing pathways and replaced the signal that should have come from the brain. With a complete network and a skilled user, resistance might become impossible before the victim understood what had happened.

He glanced toward Sasuke before continuing.

"It can also carry genjutsu directly. As long as the nerve remains inside a living target, ordinary release methods cannot avoid the illusion. The connection guarantees contact."

Sasuke's Sharingan tracked the fine chakra moving through the sample.

"The third capability is the most extraordinary," Kabuto said. "The nerve can extract information from living bodies and inanimate objects. Taijutsu, ninjutsu, secret techniques, physical changes—if the creator is close enough and wishes to know, the network may place all of it within his reach."

Experiments on discarded sealing tools showed that the fibers responded to stored chakra patterns. Tests against cultured tissue recorded changes in muscle activation and elemental affinity. Kabuto could not reproduce the distant reading without the original technique, but the material itself proved that both kinds of information entered the network.

Even after completing the experiments, Kabuto sounded incredulous. The material looked like an ordinary human nerve, yet its applications covered tracking, control, illusion, and the theft of biological information.

"Would the creator know that we removed it?" Orochimaru asked.

"The nature transformation suggests that detailed extraction requires the target to remain inside the user's sensory range. At this distance, the surviving nerves probably provide no more than a tracking connection."

Probably.

The word hung in the laboratory while Sasuke watched the living branches feed.