Ren suspected that Orochimaru possessed other versions of the Nerve Activation research.
The dark-green scroll covered only part of the human nervous system. If the incomplete technique's missing limbs and organs represented undeveloped modules, then Orochimaru likely had additional research corresponding to at least some of them.
Obtaining those records would be extremely difficult.
Orochimaru had shown Ren the second revision only because he found Ren's understanding interesting. That did not mean he would freely hand over every result produced by years of research.
Even the technique currently in Orochimaru's possession was probably still incomplete. Unless he continued developing it to completion and then taught Ren without reservation, it would remain impossible to fully reconstruct the personification inside the Gala System.
Such generosity was not entirely impossible.
Years later, Orochimaru would teach Sasuke an enormous number of techniques and provide him with resources unavailable to most shinobi. Unfortunately, that "generosity" came with the minor condition that Orochimaru intended to steal Sasuke's body.
Ren had no interest in receiving similar treatment.
"Forget it. I'll study what I have and ask Lady Tsunade for advice later."
Nerve Activation's favorability was currently limited to twenty-five, but even reaching that temporary cap would take time. There was no need to immediately solve every missing component.
"I'll unlock the first-stage trait before worrying about completing the whole technique."
Having made his decision, Ren carefully rolled up the dark-green scroll and returned it to its original place.
He took one final look around the underground archive.
Thousands of scrolls filled the towering shelves. Some contained failed experiments, others recorded dangerous breakthroughs, and many had probably never been seen by anyone outside Konoha's highest ranks.
The entire chamber felt like a tomb built for knowledge too dangerous to bury and too valuable to destroy.
Ren turned away and left.
By the time he emerged from the Konoha Research Institute, the midday sun hung directly overhead.
Its warmth felt almost unreal after three days beneath the ground.
Later that afternoon, the southern training ground rang with the relentless sound of metal striking metal.
Clang! Clang! Clang!
The impacts came so quickly that they merged into one continuous metallic shriek.
Two figures occupied the center of the field.
One remained inside a space less than three meters wide, his blond hair flashing beneath the sun as he calmly wielded a single kunai.
The other figure appeared everywhere.
Ren activated Death Mark, an offensive application of Phantom Stage, and his body blurred from sight.
A white shadow appeared on Minato's left.
His short blade slashed toward the ribs.
Minato turned his wrist and caught the attack with his kunai.
Sparks exploded between them.
Before the sparks touched the ground, Ren vanished.
He reappeared behind Minato, his blade driving toward the back of his shoulder. Minato stepped forward half a pace, allowing the steel to pass behind him before twisting around and deflecting the follow-up strike.
Ren vanished again.
Right.
Left.
Above.
Behind.
His white figure flickered through the training ground as though several attackers were surrounding Minato simultaneously.
Swish! Swish! Swish!
The short blade carved silver arcs through the air.
More than a month of Minato's special training had transformed Ren's physical abilities. His stamina, speed, explosive power, and balance had all improved considerably.
At full speed, he could now unleash three or four strikes every second.
Each attack came from a different angle. Throat, spine, heart, wrist, knee—Ren changed targets constantly, forcing his opponent to defend against both fatal and disabling blows.
Obito would not have lasted ten seconds under that assault.
Rin would have been overwhelmed even faster.
Most ordinary genin would not have understood what had killed them.
Minato, however, remained calm.
His feet moved in small, precise steps. He never left the narrow area at the center of the training ground, yet Ren's blade failed to touch him even once.
The kunai in Minato's hand seemed to appear wherever it was needed.
Clang!
He blocked a strike aimed at his neck.
Clang!
He redirected a thrust toward his abdomen.
Clang!
Without looking, Minato raised his kunai behind his shoulder and stopped a slash coming from his blind spot.
Sparks scattered across his flak jacket.
"Ren!"
Minato's voice cut clearly through the storm of steel.
"Your Death Mark has improved considerably, but it still isn't enough!"
Ren attacked from the right.
Minato tilted his head, avoiding the blade by less than an inch.
"This style is extremely effective against average opponents," Minato continued. "The constant changes in direction will overwhelm their perception and break their defense before they can adjust."
Ren disappeared and attacked from below.
Minato jumped just high enough for the blade to pass beneath his sandals.
"But what happens when your enemy's reactions are fast enough to follow you?"
Ren emerged behind him.
"Or when they possess a defensive technique capable of enduring the initial assault?"
Minato spun.
Ding!
The sharpest collision yet echoed across the training ground.
Minato struck the flat of Ren's blade at the precise moment when Ren was committing his weight to the attack.
The force jarred Ren's wrist.
His fingers loosened for a fraction of a second.
Minato disappeared.
Ren's instincts screamed.
He attempted to turn, but the blunt handle of Minato's kunai was already pressed against the back of his neck.
"Then this happens," Minato said.
The entire exchange had lasted less than a heartbeat.
Ren lowered his sword.
Minato stepped back and allowed him to turn around.
"I developed a technique with a concept similar to your Death Mark," Minato explained. "Its name is Spiralling Flash Super Round Dance Howl Style Three."
Ren stared at him.
Even though he had heard the ridiculous name before, listening to Minato say it with a completely serious expression remained impressive.
Minato continued as though nothing was wrong.
"Both techniques rely on high-speed movement and precise attacks to strike multiple targets. However, that kind of offensive pattern is most effective when surrounded by numerous weaker enemies."
He gestured toward the marks covering the ground.
"If an opponent can survive your initial assault, continuing to attack at the same rhythm becomes dangerous. Every additional movement creates another opportunity for them to understand your timing."
Ren looked down at his sword.
"Once they predict my next approach, they can counterattack."
"Exactly."
Minato raised his kunai.
"Against a strong opponent, speed should create the opening. It shouldn't replace the killing blow."
He lowered the weapon.
"If the enemy's defense doesn't collapse immediately, change tactics. Break their rhythm, force them to reveal a weakness, and then finish the battle with one decisive strike."
Minato's gaze shifted toward Ren's right hand.
"The technique you used to kill the scarred chūnin during the Land of Tea mission was a good example. That sudden burst of power was some kind of explosive secret technique, wasn't it?"
Ren nodded.
"Sonic Blade. It temporarily amplifies the force and speed of a single strike."
"Without prior information, even a jōnin could be seriously injured by it," Minato said. "That is the kind of finishing move Death Mark currently lacks."
Ren released Phantom Stage.
His white afterimages vanished, leaving only his real body standing on the torn earth.
Minato's assessment was accurate.
Death Mark was devastating against weaker enemies. Its rapid attacks and constant repositioning made it perfect for cutting through groups.
Against elite shinobi, however, speed alone was insufficient.
Jōnin rarely survived through physical ability alone. Most possessed defensive techniques, escape methods, sensory skills, or secret trump cards designed specifically to counter assassination.
Earth Release users could harden their bodies.
Skilled shinobi could escape with Body Flicker, clones, substitutions, or genjutsu.
Kumogakure's strongest shinobi could surround themselves with Lightning Release Chakra Mode, gaining both extraordinary speed and an armor-like defense.
Against opponents of that level, Instant Hell Formation lacked the raw lethality to end the battle by itself.
Ren needed to combine it with Sonic Blade, another amplification technique, or a ninjutsu capable of creating a decisive opening.
Minato had encountered a similar problem while developing his own combat style.
The Flying Thunder God gave him incomparable mobility, but teleporting beside an enemy did not guarantee that an ordinary kunai strike would penetrate their defense. He needed a compact, devastating attack that could be unleashed instantly without hand seals.
That need had helped inspire the creation of the Rasengan.
Ren did not possess the Rasengan.
But perhaps he could create a different solution.
An idea gradually formed in his mind.
"Minato-sensei, I heard that you're highly skilled in fūinjutsu."
Minato smiled modestly.
"I know a little."
Ren almost laughed.
Minato's definition of "a little" was probably very different from everyone else's.
"What are you thinking?" Minato asked.
Ren lifted the short blade he had borrowed from Kakashi.
"What if I engraved a sealing formula on the blade?"
Minato's expression became more attentive.
Ren continued.
"If the formula activated the moment the sword wounded an enemy, it might disrupt their chakra flow or temporarily restrict their movement."
He turned the blade, watching sunlight slide across its edge.
"Death Mark would provide the speed needed to land the first strike. The seal would weaken or immobilize the target, and then Sonic Blade could deliver the finishing blow."
The more Ren explained, the more complete the idea became.
A sword strike did not always need to kill immediately.
Even a shallow cut could become decisive if it carried a seal that obstructed chakra or interfered with movement.
The blade could also be treated with a paralytic agent or fast-acting anesthetic.
Swordsmanship would create the wound.
Poison would weaken the body.
Fūinjutsu would suppress chakra or restrict movement.
Three separate effects would activate from a single successful strike.
Even a jōnin might be unable to respond if Ren created an opening lasting only half a second.
Minato considered the proposal seriously.
"Theoretically, it's possible."
Ren's eyes brightened.
"There are fūinjutsu capable of interfering with chakra and binding movement," Minato explained. "The Sealing Method and Finger Engraving Seal contain principles that could be adapted for ninja tools. More advanced binding curse seals could produce an even stronger effect."
He held up his kunai.
"However, inscribing a formula on a weapon is only the beginning. The seal must survive repeated impacts, remain stable while chakra flows through the blade, and activate only when the correct conditions are met."
"If it activated too early, I could seal myself."
"Correct. If the formula broke during combat, it might fail completely or release its stored chakra unpredictably."
Minato tapped the side of Ren's blade.
"Creating a seal that can trigger immediately upon contact requires extremely advanced control. Most shinobi couldn't do it reliably."
Ren studied him.
"What about you?"
Minato coughed.
"I could probably design part of it, but another person would be better suited to completing the formula."
"Kushina?"
A warm smile immediately appeared on Minato's face.
"If Kushina agrees to help, the inscription won't be a problem. Her knowledge of Uzumaki sealing arts is far beyond mine."
He lifted one of his three-pronged kunai.
"She helped me stabilize the formula used on my Flying Thunder God kunai."
Ren raised an eyebrow.
"So I need your future wife's help?"
Minato nearly dropped the kunai.
"F-Future wife?"
His face flushed as he quickly waved one hand.
"Don't say things like that! Kushina and I aren't married yet."
"Yet?"
Minato froze.
Ren's smile widened slightly.
Minato coughed several times and hurriedly changed the subject.
"I'll ask Kushina whether she's willing to examine the idea. However, this sword belongs to Kakashi, doesn't it?"
Ren looked down at the short blade.
"Yes. He loaned it to me."
"Then you must obtain his permission before altering it," Minato said. "A sealing formula could permanently change how chakra moves through the metal. You can't make that decision without asking the owner."
"That's reasonable."
"There's another issue." Minato's expression became serious again. "Even if Kushina designs and engraves the formula, you'll need enough knowledge of fūinjutsu to activate, maintain, and repair it yourself."
Ren nodded slowly.
Relying entirely on another person would leave him helpless if the seal became damaged during a mission.
Minato returned the kunai to his pouch.
"I'll bring you two introductory books on fūinjutsu. Study them first, and then I'll teach you the basic principles personally."
"You're willing to teach me?"
"You're my student." Minato smiled. "Teaching you is my responsibility."
His expression then became faintly mischievous.
"Of course, that depends on whether you possess any talent for sealing techniques. If you don't, even Kushina won't be able to save you."
Ren looked at the blade in his hand.
Fire Release had given him destructive power.
Nerve Activation might eventually sharpen his reactions.
Now fūinjutsu offered a way to transform even the smallest wound into a fatal opening.
If Ren succeeded, Death Mark would no longer be a storm of harmless cuts against powerful enemies. Every touch of his blade could become a death sentence.