The next morning, Hiruzen came to the Uzumaki house—or rather, his shadow clone did. The old man looked as if he were simply out for a casual walk, but his steps were heavy and deliberate, like someone carrying not just two children, but an entire destiny. The twins exchanged a silent glance and followed him.
The road led them to an unremarkable building deep within Konoha. On the outside, it was just another administrative structure: gray stone walls, windows tightly sealed with curtains that only let sunlight glimmer dully, as if hinting that something hidden inside wasn't meant for outsiders. The door bore no markings either—no plaque, no seal, no sign of purpose. A ghost house in the middle of a living city.
"My grandchildren," Hiruzen began in a raspy voice, lighting his pipe with practiced ease. At once, the air filled with the sharp tang of tobacco. "To become a sensor, one must walk a long and difficult path."
He spoke as though lecturing, and even the gray haze of smoke seemed to underline his words.
"In time, every strong shinobi learns to feel foreign chakra. But the way to that skill differs. Some rely on a natural gift or a kekkei genkai. For instance, the Byakugan is a sensory dōjutsu in itself. The Inuzuka's nose or the Aburame's symbiosis with insects don't directly count as classic sensing, but yield a similar result. Others turn to the elements: some feel the tremor of earth, others sense shifts in the wind, or moisture in the air. And then there are the rarest of all—those who perceive the whole of nature as a single organism."
Naruko listened wide-eyed. Menma wasn't far behind her in attention. Whatever else could be said about the old man, he knew how to make a story interesting. A true Professor.
"We'd like to learn the most common sensory technique," Menma said, deciding it was time to steer the talk back to practice. "Mizuki-sensei claimed it's something anyone can learn."
Hiruzen's gaze lingered on him. He half-closed his eyes, then, exhaling smoke with an air that mixed irony and something like weary mockery, said:
"What well-read, knowledge-sharing teachers we have at the Academy… Interesting. I suppose Mizuki himself isn't a sensor?"
"No," the twins shook their heads in unison.
"A cobbler without shoes," the old man snorted, releasing another cloud of smoke. "Keep in mind: the most common technique also means the most common countermeasures. Which is why, children, in time you'll need to supplement it with something of your own."
[For example, Ashura's unique kekkei genkai. Thanks for the hint, old man. But I've got my own methods.]
"But tell me, Menma," Hiruzen narrowed his eyes, leaning forward to peer into the boy's, "if, as your teacher claims, anyone can master sensory skills, then why isn't every shinobi in the world a sensor?"
The boy paused only a moment.
"Probably because there's a hidden condition in that training. Learning to sense isn't the same as learning to walk on trees."
A thin, almost approving smile touched the old man's lips.
"Correct. The art of sensing is comparable to a clan's hiden jutsu. Formally, anyone could learn it, but—" he waved his hand, "clans rarely share such secrets. They don't want their allies becoming stronger than themselves."
[Ah, here we go: clans are greedy, secretive, shortsighted. Perfect groundwork to justify the 'great altruism of the Hokage,' who will, of course, generously share his knowledge.]
But then Hiruzen's tone shifted.
"And yet," he took a long drag and exhaled slowly, deliberately, "the reason sensory training is withheld isn't greed. The real difficulty is that not everyone can withstand the basics of it."
"But sensing doesn't involve heavy strain," Menma objected, crossing his arms.
"Physical strain—no," the old man nodded. "But who better than you to know that mental overload can be far worse."
The twins' faces flickered with unease, and Hiruzen clearly savored the moment.
"Ever heard that when someone loses their sight, their other senses sharpen?"
"Yes," Naruko answered first. "Hearing, smell… everything gets stronger."
"Right. Now imagine this—if a shinobi is deprived of all five senses at once, his sensitivity to chakra multiplies. Originally, it was a torture method," Hiruzen said grimly. "In ancient times, enemies were stripped of sight, hearing, taste, smell, and touch. Locked in utter darkness and silence, left alone with themselves. Few lasted more than a few days. Most broke and would spill any secret just to avoid returning to the deprivation chamber."
Naruko shivered.
"That's… horrible."
"Effective, though," Hiruzen added without a trace of shame. "And the most curious part—some prisoners truly awakened sensory abilities afterward."
"And you turned that into training?" Menma asked cautiously.
"Precisely." The old man laid his palm on the cold stone wall of the building. "That's why this place was built. Here they bring only the most resilient, the most stable, and the strongest-minded shinobi of Konoha. Inside, a person is placed into a special iron coffin. Thanks to fūinjutsu, all senses are stripped away. No light, no sound, no touch. Even the sense of your own body disappears. It feels as though you're floating in a void. And only then… only then do you get a chance to feel foreign chakra."
The wind tugged at the edge of Hiruzen's cloak, making his figure seem even grimmer.
Menma swallowed.
"And how long… do you have to stay in there?"
"Until you can sense at least one of the attendants on duty outside," he replied calmly. "Sometimes days, sometimes weeks."
"I'm ready!" Naruko shot her hand up so sharply it looked like she'd been called to answer her favorite question in class. "Gramps, lock me inside! I wanna finish the training before Academy break is over!"
Hiruzen narrowed his eyes and sighed, as if seeing someone else's shadow in her. His hand rested gently on her head, but the gesture carried no warmth—only condescension.
"Naruko-chan, you're just as impulsive as your mother."
Naruko squared her shoulders proudly, as if she'd heard a compliment.
"I already told you—originally, this was a torture method." Hiruzen took a drag of his bitter tobacco. "A shinobi was left alone in the dark, face to face with his demons. Only if he found the strength to grasp that new sense did he have a chance to survive and turn torture into training. But it took time… a day, a week, a month. Some lost their sanity before awakening sensory skills."
His voice carried no pity, no horror—just a cold fact.
"Gramps," Naruko suddenly asked, frowning. "How long did it take you?"
"Eight days," Hiruzen answered calmly, exhaling a puff of smoke. "And afterward, it took me half a year to restore my mind under Tobirama-sensei's supervision."
The words hit the twins like a bucket of ice water.
[Sure, I want to become a sensor… but to crawl willingly into a torture coffin for it? No thanks. And if this really is the basic method, that means Karin went through the same. Well, no wonder she was half-crazy in canon.]
"I don't get it!" Naruko burst out, like someone had thrown fuel onto her fire. She jabbed her finger right at her grandfather. "Did you drag us here just to scare us instead of teaching us?!"
Hiruzen smirked at the corner of his lips without removing his pipe.
"I admit, that was the hope. I can't expose my own grandchildren to such a risk for their minds."
[But you had no trouble turning the entire village against us, did you, old man?]
"Gramps!" Naruko clenched her fists, her cheeks burning red with anger. "How are we supposed to become strong defenders of Konoha if you keep holding us back?! How will we protect you when we grow up?!"
A soft, almost fatherly smile appeared on the old man's face.
"Heh. My protectors."
[That's what I love about her. Real, pure faith you can't fake. Old schemers fall for it every time.]
"But still," Hiruzen went on, growing serious again, "I'm the Hokage right now. And it's my duty to look after the health of our citizens."
"So," Naruko narrowed her eyes, planting her hands on her hips, "you're not going to keep your promise?"
"Now, now," Hiruzen took a long drag, a smile flickering on his face. "I'd never deceive you. But perhaps it's worth waiting a bit? Say, until you graduate the Academy…"
"Five years from now?!" Naruko exploded like a firecracker. "I'll start a hunger strike right this second!"
Menma lazily added, as if offhand:
"Besides, our father went through the training at about the same age."
The old man averted his eyes for a moment, as though calculating something, then spread his hands.
"Well, I tried…" He even smiled almost boyishly. "Since you won't be stopped, I've devised a safe limiter to protect your minds."
"Shadow clones," Menma understood at once.
"Correct," Hiruzen nodded. "Every day, new clones will be created and placed in deprivation chambers. But no memory transfer! Otherwise you'll go insane. Each clone must search for the path anew, again and again. It's slower than the real training… but much safer."
"I'm ready!" Naruko blurted out again, already forming the seal.
But Menma gently set his hand on hers.
"Make only as many clones as will still leave them chakra to actually train sensing."
"Smart thinking, Menma-kun," Hiruzen blew another smoke ring. "Sensory techniques require chakra too. The more reserves your clones have, the longer they can search for the answer in a day."
"Got it," Menma nodded and created five clones.
Hiruzen slowly led them into the building. The originals stayed outside, in the sunlight. But the clones wore grim, doomed expressions. They knew they weren't heading for training, but for execution.
And in Menma's chest, a cold knot of guilt stirred.
[I just created them and sent them off to suffer. For the sake of my own power. Welcome to the shinobi world.]
///
Two weeks passed since the start of their sensory training—and the results looked dismal.
Every day the Uzumaki twins made clones, every day those clones were sent into the deprivation chamber. And every day, half of them came back broken. Some literally—clones bursting out wild-eyed, lunging at attendants like rabid beasts, forcing them to be restrained by force. The other half looked only slightly better—glassy stares, trembling hands, incoherent words. To them it felt as though they had spent not hours inside, but years—an entire lifetime in total void.
Naruko suffered most of all. For someone so talkative and loud, even brief isolation was torture, let alone absolute darkness and silence. Her clones almost always snapped. Every day she watched them stumble out with empty eyes, and every time it struck her heart like a blow. She tried to mask the worry with her usual bravado, but Menma could see it—this weighed on her far more than she would admit.
Worst of all: no results. Not a single clone, no matter how much they suffered, managed to sense the presence of the observers beyond the wall. All their efforts sank into nothing.
The only consolation was that, by listening to the scattered reports of the few who remained half-sane, Menma could at least start discarding useless approaches.
In the third week, a spark of hope appeared. One clone, barely coherent, reported seeing vague silhouettes in the darkness—like flickering candle flames. Whether it was chakra or just hallucination, he couldn't say. But it was something.
Menma absorbed the memory. The recollection of isolation flooded his mind in a cold wave—pain and sticky terror. But unlike the clones, he viewed it from the outside, like an audience watching a film. His psyche remained intact, though afterward he was haunted by nightmares of endless darkness.
The path to sensory mastery continued.
To distract themselves, the twins switched to physical training. Fortunately—or unfortunately—Konoha had just welcomed back the Green Beast from a mission.
"Do as I do!" roared Might Guy, standing on his hands and doing push-ups hard enough to rattle the earth. A boulder the size of a man's torso was tied to his legs. "Real training begins only when you're ready to faint from effort!"
"Yes, Guy-sensei!" shouted a sweat-drenched Lee, copying the exercises with fanatical devotion.
"Don't slack, Bushy Brows!" Naruko barked, barely keeping her balance on her hands but refusing to give in. "I'll out-push-up you!"
"Now that's the spirit!" Guy bellowed, his eyes blazing with literal fire. "I can feel the power of youth burning within you both!"
Menma kept up in silence, saving his breath. His face was calm, but every muscle screamed in pain. After losing Kurama, everything was harder. Ashura's kekkei genkai helped—his body could endure better than even Rock Lee's—but without the regeneration of a jinchūriki, he had to pay for every workout with long hours of recovery. No more fifteen-minute breaks in the grass to bounce back fresh and strong. Now the price was real.
Soon Lee collapsed mid-push-up. Even the Curry failed to revive him a second time. Beaming with pride, Guy hoisted his student onto his shoulder and galloped toward the hospital, loudly promising that tomorrow would bring them a fresh helping of suffering—er, training.
The twins lay sprawled on the warm grass, too exhausted to move. The sky above was slowly darkening, the air smelled of sweat and dust, and their own bodies felt like sacks of sand.
"Maybe we should crawl to the hospital too?" Menma muttered, barely able to move his tongue.
Naruko stayed silent for a long time, then forced her head to turn toward him and rasped:
"Nah, no strength to crawl that far. Let's just lie here for an hour… then somehow drag ourselves home."
"Mmm, yeah," Menma groaned, staring at the sky. "Shame neither of us is a medic-nin. We could've healed each other in no time. We still have plenty of chakra…"
[Wait. We're pure-blooded Uzumaki. We don't need a medical license to heal. Hm… what if I try?]
Before he could think it through, he suddenly grabbed his sister's arm and sank his teeth into it.
"Kyyaaa!" Naruko shrieked so loudly that a flock of sparrows scattered from the nearest tree. "What the hell are you doing, you psycho?!"
But at that very moment, Menma felt a surge of vital energy wash through his body. Fatigue vanished, muscles filled with strength, pain receded. Within seconds he was already on his feet, as if he'd never been half-dead in the grass.
"It… works," he muttered in astonishment.
[Uzumaki Karin's healing method works!]
But he didn't get the chance to explain. Because Naruko, blazing with outrage, instantly bit into him in return, hard enough to make him yelp.
Her body was immediately wrapped in a green glow. Menma clearly felt part of his chakra flow into her, followed by her relieved sigh.
"Holy crap!" Naruko flexed her fist in excitement. "Nothing hurts! At all! Bro, how did you even think of this?!"
"Sudden inspiration," he waved lazily, hiding a pleased smirk. "By the way, did your arm heal?"
"Yep!" she proudly showed off smooth skin without a mark.
"Well, mine didn't," Menma held out his arm with fresh bite marks. "Guess I'll have to heal myself…"
They quickly ran a series of "experiments"—taking turns biting each other and studying the effect. They discovered that yes, the bite healed wounds, but whoever was bitten last always kept a scar. Not exactly pleasant.
"So it only works with a deep bite, when Uzumaki blood is taken," Menma mused, examining the fresh mark on her arm. "Hm. What if we try another fluid?… Sister, open your mouth."
Naruko instantly narrowed her eyes.
"Why?"
"Trust me. Have I ever done you harm?"
She squinted, clearly remembering his bite from five minutes ago, but after hesitating, obeyed.
And then Menma spat straight into her mouth.
"Cough—cough—what the hell?!" Naruko choked and spluttered. "Are you insane?!"
"No, no!" He clamped her jaws shut with both hands. "Swallow!"
She tried to spit it out, but he pinched her nose shut. Agonizing seconds of struggle passed, and only when Naruko turned blue from lack of air did she gulp it down with a loud sound.
At once her body flared with green light.
"Magnificent!" Menma threw his hands up in triumph. "Perfect! Now we can train with Guy without worrying about scars!"
But Naruko didn't share his joy. She slowly wiped her mouth, looked at her brother with a gaze that would make a sane man's hair stand on end, and sweetly said:
"Brother… let's play theater."
"Uh… what roles?" Menma had already taken a cautious step back, sensing the storm.
Naruko bared her teeth like a cat about to pounce.
"You're Madara. And I'm Hashirama. And this is the final scene… where I kill you!"
"Oh, crap," was all Menma managed to say before spinning around and sprinting for his life.
[Ehh. I'm starting to understand why Orochimaru fled Konoha. Hard to do science when everyone around you is so damn touchy.]