The reverse summoning light faded, leaving them in silence and heavy, wet air.
A dim green mist clung low to the ground, glowing faintly as if alive.
The warmth carried a hint of acid, stinging faintly at their skin.
Beneath their feet, the surface shifted with each step, soft, yielding, almost pulsing, like walking over the flesh of something that hadn't decided whether it was soil or living tissue.
Every step sent faint ripples through the ground, spreading and shimmering before fading, like chakra moving through living clay.
Nagato stood still, his hollow gaze unmoving as his chakra sense spread outward while his eyebrows furrowed.
The world around him trembled with life, layer upon layer of dense, overlapping energies that filled every inch of space.
"This energy…" his voice was low, uncertain. "It's not chakra. Not human. Not even animal. It's everywhere. And this… isn't normal terrain."
Ryusei's tone was calm, almost casual. "That's because it isn't. You're standing on something halfway between earth and organism. Try not to think about which side wins."
Around them, bone-white pillars curved upward like trees, translucent and faintly pulsing.
Droplets ran down their surfaces, sizzling softly as they touched the ground.
The air was thick, warm, and carried the sour tang of something breathing.
Beneath it all came a low, rhythmic sound, a deep pulse echoing through the mist, steady and patient, like the heartbeat of the world itself.
Ryusei looked composed, but the faint flicker of awe in his eyes betrayed him.
The first time he came here, he'd thought that pulse was genjutsu.
Now he knew better.
The forest wasn't just alive—
It was Katsuyu, or at least other 'parts' of her, spreading through every root, every pulse beneath their feet.
Nagato spoke again, his tone quiet, almost reverent. "This constant pressure… So, is it natural energy? It feels endless."
"Not ordinary natural energy," Ryusei said. "This place holds one of the highest densities in the world. You can sense it right away like that only because it doesn't try to hide."
He paused, then added lightly, "And don't breathe too deep. The air here is mixed with corrosive vapor. If your control slips, you'll burn from the inside."
However, before Nagato could respond, the ground ahead massively rippled out of the sudden.
The mist thickened and split open as something colossal rose from below.
A mountain-sized slug, translucent and glistening like liquid crystal, emerged with slow, effortless motion.
A weight of energy so immense that Nagato could feel its edges curving around him, enveloping the entire clearing.
Her surface shimmered with pale blue light, and her voice came not as sound but vibration, a calm, layered echo that seemed to speak through their bones.
"Ryusei… again."
The sound was weary and recognizable: patient, tired, and faintly exasperated.
"You never come empty-handed," she said after a pause. "And another human this time. Let me guess, not a gift, but another problem you're leaving me with."
Ryusei smiled faintly. "Come on, Katsuyu. He's the one I recently told your fragments about. Figured he could use a change of scenery. And deep down, you like the company, no point pretending otherwise."
One of her massive eyes blinked with slow irritation. "Like is a strong word. Tolerate, maybe. But I'll admit, you're more amusing than most of the last few hundred who came here just to dissolve and die soon."
Nagato muttered, still struggling to process the scale of her true form and pressure, and how casually Ryusei was talking to it. "This… is Lady Katsuyu?"
Ryusei nodded. "The real one. The parts I summon usually are just fragments. The rest stays here."
Katsuyu's massive body shifted slightly, and the ground quivered in response.
"So, this is the one you're vouching for? He doesn't look suicidal enough for this place."
Ryusei's tone stayed calm. "He's very strong. He has a powerful Sage Body tier physique already."
Her feelers twitched. "Strong won't help him around here. You should know how this works already."
"I know," Ryusei said, still smiling. "But he's not like the others."
Katsuyu's voice oddly softened at that, with a sigh that seemed to move through the air itself.
"I heard that many times; they always say that before the screaming starts, and I watch someone dissolve again."
The mist thickened around them.
Nagato ignored the comment and, meanwhile, just sensed into the distance, where the pillars bent and curved like frozen waves. "So this… is where I'll learn?"
Katsuyu's tone turned dry. "Learn, suffer, dissolve, the order's up to you. Shikkotsu doesn't teach. It absorbs. The ones who survive just learn not to vanish."
Ryusei chuckled. "Don't listen to her. She's just shy."
"I'm lazy," Katsuyu corrected. "And tired of cleaning up after you.
"But he might actually survive this one."
Her voice rippled through the air like a sigh. "If he doesn't, I'm not burying him."
Ryusei smirked. "You don't bury anyone, Katsuyu. You absorb them."
"That's exactly my point."
The mist thickened again, curling around them like breath.
Katsuyu's tone softened, only slightly. "You still want to proceed, even knowing where you stand?"
Nagato inclined his head. "If it's possible, I'll endure it."
"Possible," she repeated. "That's a generous word for this place."
Ryusei folded his arms, his tone casual but his eyes sharp. "Then let's find out how generous it really is."
Another sigh, long, slow, resonating through the forest floor itself. "Fine. I'll allow it. But don't say I didn't warn you both."
"You always warn me," Ryusei said lightly.
"And you never listen," she replied. "One day, that'll be interesting."
...
Soon, they moved deeper into the forest.
The mist grew even heavier, clinging like liquid air.
Every few steps, the ground fully sank and reshaped, swallowing footprints whole as if unwilling to let anyone pass cleanly.
Even without eyes, Nagato could sense how the environment shifted.
The deeper they went, the more it pulsed, the air vibrating with even more invisible tension.
The very humidity felt alive, saturated with energy that pressed softly yet endlessly against their skin.
Occasionally, skeletal remains jutted from the surface, half-melted shapes barely recognizable as human.
Each bone was porous and translucent, as if digested over the years.
The terrain accepted them without distinction, drawing their last traces of chakra into itself.
"The forest remembers everything," Ryusei said quietly. "Nothing dies here. It just changes form."
"Those were all…?" Nagato also began sensing something was amiss about it.
"Previous guests," Ryusei said. "The impatient kind."
Katsuyu's low vibration rolled through the ground. "Hundreds over the centuries. So many convinced they were chosen."
A faint rumble followed, almost like a chuckle. "The forest took them all before they even reached the core. Efficient, in its own way."
Even her voice carried that calm, detached boredom, like someone long past any surprise.
She knew the only reason Ryusei and Nagato could even reach the core was because of their bodies' sheer durability and the immense life force pulsing through their vast chakra.
They continued forward.
The bone pillars began to curve inward now, translucent membranes stretching between them.
Drops of acid fell from above, sizzling when they struck the ground.
Closer to the center, the air thickened until each breath came heavy.
The mist shimmered faintly, green and gold threads moving through it tirelessly like veins.
Nagato's body tensed. "It's like breathing very nature itself…"
"Careful," Ryusei said. "Too much, too fast, and you'll stop being you."
Katsuyu's voice echoed faintly ahead of them now, resonating through every surface. "He's right. You don't balance nature here; you surrender to it. That's why no one stays whole."
Nagato tilted his head, listening to the pulse beneath the ground. "Then why so many still do it?"
"Because those who survive stop being human," Ryusei said. "And the power is worth the risk."
They reached a wide clearing then, where the mist parted enough to reveal a shallow basin.
Black liquid filled it, thick and still, not reflecting any light.
It pulsed faintly with the same rhythm as the ground beneath their feet.
Katsuyu's tone dropped, quiet and steady. "The Black Pools. Everything that dies here ends up there: flesh, chakra, and memory. It's the forest's core. Its lungs. It's stomach."
Nagato could feel it clearly even without sight.
The pool wasn't water.
It was alive, layered, ancient, full of whispers.
"Some of the strongest natural energy in the world gathers here," Ryusei said, his tone almost reverent.
"But it's mixed with everything else this place has ever consumed. Every drop carries both power and death."
Katsuyu's feelers shifted, stirring the mist like slow waves. "He's not wrong. Every failure leaves a trace, flesh, chakra, or even will. The more who come, the heavier the air becomes, until even breathing here is a test. The forest remembers all of them, and it punishes impatience."
Nagato tilted his head slightly. "So the more that failed, the harder it becomes now… and if one succeeds?"
"Then the forest gives back a fraction of what it's taken," Katsuyu said. "You don't simply gain Sage Mode, you're remade. Body, chakra, and essence, all reforged through dissolution. That's the reward, if you insist on calling it that… from a human point of view, at least. Provided you survive being digested."
Her massive form shifted faintly, and the ground trembled beneath them. "To do it correctly here, you don't draw energy in like at Myōboku or Ryūchi Cave. You let yourself dissolve into it. The forest decides whether you return. Simple."
Ryusei sighed softly at her half-answer first, and then calmly filled in the rest for Nagato, knowing Katsuyu was far too lazy to explain anything past a few basic sentences.
Unlike Toad Sage Mode, which centered on balance, or Snake Sage Mode, which embodied domination and rapid adaptation, Slug Sage Mode was entirely different.
It wasn't about control at all; it was about surrender.
Gradual immersion without dissolution.
The user had to let themselves merge with the forest's natural energy, become part of it, and simply endure.
No resistance, no shaping, just survival through stillness, allowing the energy to rebuild what remained.
Nagato eventually gave a faint smile toward the gigantic slug after taking in Ryusei's full explanation. "That's your definition of simple?"
"It's efficient," Katsuyu replied evenly. "And quiet when it fails."
Ryusei folded his arms, eyes narrowing slightly. "Only one man ever completed it in recent history, Hashirama Senju, the First Hokage. The closer you look through time, the worse the odds get. Some lasted minutes… most barely seconds. It's extremely difficult."
Katsuyu exhaled, her voice softening to a low, vibrating sigh that rolled through the basin. "Difficult? You mean fatal. But fine. I'll allow it. If he dies, at least it'll keep the pools fresh for a while."
The black water stirred as she spoke, ripples spreading outward like breath.
The mist thickened again, faint light shimmering across its surface.
"Welcome, Nagato," she said, her tone calm and final.
"To the only place in this world that decides who truly belongs to nature… and who was only pretending."
Nagato stood silently at the pool's edge, the humid air stinging faintly against his newly healed skin.
The faint ripples of the black surface reflected nothing, just an unending, shifting void.
Ryusei's words lingered in his mind, steady and matter-of-fact, as if describing a weather pattern rather than a graveyard of failures.
Hashirama Senju… the only one. Of course, Ryusei knew the odds. He wasn't sending Nagato first out of trust—he was studying.
It made sense. Ryusei was younger, his body still growing, refining; this was data he needed before attempting it himself. And Katsuyu, that ancient creature who somehow tolerated him, likely knew it too.
Nagato didn't feel angry about that. There was no room left for that kind of emotion. Gain had never come without risk; he'd learned that long ago. The world was nothing but exchange, pain for strength, loss for understanding.
He could feel it now, clearer than ever: the immense power flowing beneath this place.
The pulse of the forest made his chakra tremble.
Compared to this, his Rinnegan, that legendary gift from the gods, felt small.
Even the memory of that glowing-eyed being who had crushed him before, insignificant next to this endless, sleeping will.
He almost laughed at the thought.
'So this is what true power feels like, he thought. And I called myself a god.'
The realization settled cold in his chest.
All those years spent clinging to Yahiko's dream, shaping pain into faith, thinking he was remaking the world, he had been little more than a puppet.
A weapon guided by the masked Uchiha's unseen hand.
Now, there was no grand purpose left.
Just quiet resolve.
Protect Konan.
Avenge the people of Ame.
Find out whether those who had manipulated his life so completely were truly behind it all, and if they were, see Yahiko's vengeance through to the very end.
He exhaled slowly. The air burned his lungs faintly, but he didn't flinch.
Pain had long since become background noise, constant, familiar, almost rhythmic.
It had shaped him, defined him, carved his identity into something unrecognizable.
Not just emotional pain, literal, unending pain that never once left his body.
Recently, every breath, every heartbeat, had come with the sting of those black rods buried in his flesh, the Rinnegan draining him a little more each day.
He hadn't just felt pain.
He had been the Pain.
So, when he stepped forward and the black water lapped at his ankles, eating softly through skin that immediately regenerated, he didn't stop.
The heat, the sting, the slow, creeping dissolution, it all felt familiar.
He took another step.
And another.
Ryusei watched in silence from the edge, his expression unreadable and rarely completely serious nowadays.
He knew that Nagato had at least a decent chance of succeeding.
His willpower, hardened by a lifetime of loss, was exceptional, the kind that could endure pain, resist despair, and confront the vengeful remnants that would try to drag him under.
Physically, he now carried a true Sage Body, and a rare fusion of Senju and Uzumaki vitality.
His chakra was vast, his body reinforced, and his chakra control refined from a long time of remotely operating the Six Paths of Pain avatars and other similar chakra technologies from inside the Amegakure.
So, all the conditions were there, at least in theory.
Still, there was no certainty here.
There had only ever been one Hashirama, and this was undoubtedly the most unforgiving and mysterious Sage Mode and power-up in general, in existence.
Even he wasn't sure he could master it, that was why he'd waited so long.
So how could he be sure about Nagato?
The only thing certain was that this would serve as the best possible gauge, a way to measure how far he still was from attempting it, and how to refine his own approach when the time came.
His micro-quake training pulses were steadily refining his body, strengthening it faster each week, narrowing the gap, despite his way younger biological age.
He just didn't know when the risk would be acceptable, soon enough to matter, but not so soon that it killed him.
With whom, or what, he was up against, he needed this power as quickly as possible… but one wrong step here could mean instant unforgiving erasure instead of evolution.
So, beneath the eyepatch, his lone Byakugan constantly pulsed faintly, recording every flicker of chakra, every reaction, every microscopic shift of Nagato's body in real time.
Katsuyu's immense eyes remained half-closed, her voice rumbling low and detached through the mist.
"Another one walks willingly," she murmured. "Let's see if this one remembers how to come back."
Nagato said nothing.
He simply kept walking until the blackness reached his waist, his chest, then his throat—
and the world began to hum.