Danzō had built ROOT beneath Konoha partly to justify the name and to force any intruding groups to feel lost in the old utility tunnels and sections of the village that had been rebuilt sometime in the past and then promptly forgotten. Even most, if not all, ANBU members would have walked past the access points they used without realizing anything was going on beneath their feet.
"There." Fugaku appeared between two houses whose occupants were already asleep, pointing at nothing but trash bins in the narrow alleyway, leaning against a simple wall.
"You're sure?" Jiraiya asked, appearing just as silently right behind him.
"..." Fugaku's Sharingan rotated slowly as he gazed at the spot, then looked over his shoulder at him. "No. But something is off."
"I can't sense anything," Sakumo appeared next, taking a deep breath, scanning the same spot.
"The wall is real." Ashina joined the group next. "But it has a seal and a room behind it. A simple cluster-barrier... Hm. Allow me!" He added as he walked past them, already forming seals, doing it so quickly that Fugaku could barely track them all with his Sharingan.
CRACK!
The concrete wall split down the middle the next moment and began sliding apart, knocking over the bins and revealing a corridor leading underground. The moment it happened, a kunai came from the darkness before anyone could say anything. Sakumo reacted first, drawing his short blade and surrounding it with white chakra, deflecting the kunai and splitting it in two as the pieces struck the side walls.
However, the one who threw it didn't remain hidden as they came at them without shouting or warning. A second later, twelve masked shinobi spilled out of the hole and attacked the group. The first wave of them threw weapons out, connected by wires, while the second sent forth wind-based jutsus, their coordination easily matching any ANBU member, even overshadowing some of them.
Sakumo, unflinching, still welcomed the attacks as his blade became a beam of white light. No matter how short his sword was, the attack he released was wide enough to consume all the thrown weapons, slicing them into millions of pieces along with the wires.
"Earth Release: Earth Wall!" Jiraiya had already slammed both hands down by then, and a stone wall rose to block the wind blades, while also boxing in the ROOT operatives.
By the time they skidded to a halt, Fugaku was already behind them, catching one of them, stabbing a simple kunai into the man's neck, killing him, before looking into the eyes of the first, who managed to turn around. Just a stare was enough, making the man raise his hand and jab his own fingers into his throat, killing himself. While the two bodies were falling over, Fugaku had also finished his seals, breathing fire at the group, setting them ablaze... Yet none of them cried out even then.
"Alive!" Jiraiya yelled, dousing them with water. "We need them alive!"
"That won't be happening," Ashina stated, before Fugaku could say anything. "Look."
"Dead...?" Jiraiya asked, as the earth-made wall disintegrated and they began checking the smoking bodies. No wonder they didn't yell... they were dead, their skin already black, and not from the fire.
"Poison," Sakumo muttered, kicking one over onto its back. "They killed themselves when realizing they lost..."
"Tsk..." Jiraiya glanced over the corpses, angry that they were wasting precious lives when the Third Shinobi World War was just starting.
"No time to dawdle," Fugaku said, heading into the dark corridor. "Let's hurry before he escapes! We can capture him and then get to know everything."
He wasn't wrong, but the deeper they went, the harder they had to fight. Fugaku had seen good shinobi before, both as allies and enemies, and even he had to exhale in frustration, because the one-eyed bastard did collect capable and promising subordinates. And they were now massacring them in the dozens... Whenever one of their masks fell off... they looked barely older than 16 or 18... They were promising kids, with eyes that already held no light at all.
No matter what they tried, be it a jutsu or an explosive tag, Fugaku and Sakumo passed by the silent operatives before their jutsus even finished. Either a line of white chakra slashed them up, or a flash of red from Fugaku's Sharingan brought their ends, as they soon lay on the ground, dead. Even if they didn't kill them, they killed themselves, sometimes even exploding their own bodies.
It was like that when Ashina's chains captured one of the attackers, pulling him closer, ripping the mask off his face.
"Where is Danzō?"
"..."
"Where?!"
The operative's tongue began glowing and growing just then, and if not for Ashina being decisive, flinging the body into another ROOT Shinobi, the man's body would have exploded into his face... Now it did so to his comrade, taking him along to the afterlife instead.
After they descended even further, their damned hideout turned out to be well built... They discovered that in the second layer they reached, right when the floor disappeared from under them. Naturally, something like that didn't bother the group, as Sakumo simply stuck himself to the ceiling, using it as the new floor, while Fugaku and Jiraiya simply stood on the wall.
"Poison," Ashina said, using his chains to create a spiderweb and hang down from it. "I can smell it... One stab and even I would be in danger." He muttered, watching the tiny needles down below. "I rate this... Hm... Mediocre."
"You're grading the traps?" Jiraiya asked, shrugging, shaking his head.
"Someone should." He answered calmly, looking at the others. "He wanted to be the Hokage. I am evaluating how far he is actually from the position, and so far... He is at best a low-level Jōnin." The moment he finished, the walls shook, and fire poured in... or it tried, but Ashina already sealed the holes the moment they appeared, keeping the flames within. "As I said. Mediocre."
"We should move." Fugaku's Sharingan moved, ignoring the fire, already discovering their new route, heading forward, followed by the others, who were unable to hide some smiles thanks to Ashina's commentary.
When their group finally broke through and entered the fifth layer, deep beneath Konoha, they landed not in another trap, but in a room, their eyes immediately identifying Danzō, who stood behind a stone desk, almost as if he were waiting for them, cane in one hand.
"Sakumo..." He addressed the only one he was now looking at with his one eye.
"Danzō-sensei." Sakumo's expression didn't change as he answered, and he remained polite, but they both knew it was only because of their brief time as master and disciple.
"You should know better than to participate in this."
"I only know that I'm doing the right thing," Sakumo answered, making the old man's hand tremble on his cane.
"You were taught what happens when a village fractures during war. Are you throwing my lessons away? I thought better of you. Stand aside... It is still not too late."
"No."
Danzō's chakra surged at once as Fugaku's Sharingan spun, speaking before the man's cane could come apart.
"Move!"
Danzō's attack was a blade that emerged from his cane, followed by a jutsu from his mouth, aiming at the group as a whole.
"Wind Release: Vacuum Sphere!"
The chamber was swarmed with bullets of compressed air, and they both had to dodge while fending off Danzō's strikes with his blade... which made Ashina get hit when a sphere struck his shoulder.
"Hm." He muttered after skidding to a halt, looking down at his torn robes and the adamantine chains beneath them, covering his body like armor. "Ouch."
"Wind Release: Vacuum Great Sphere!"
Danzō wasn't stopping, of course, sending more attacks at Ashina, wanting to at least eliminate someone who was probably the weakest. At least, according to his ROOT agents' reports, he used the most chakra to escape and was still recovering. Alas... He underestimated the vehemence and recovery rate of a genuine, pure-blooded Uzumaki's chakra. His jutsu struck Ashina's chains, only having enough effect to turn him half-naked, but draw no blood, while exploding the wall behind the old man.
Changing targets, Danzō was now aiming at Jiraiya, swinging his cane sword at him. He leaned back at the last moment, the tip of the weapon cutting his cheek open, while the rest of his body was protected by his enveloping white hair, turning him into a hedgehog. He wasn't done either, as those needle-like strands shot out next, causing Danzō to back off and defend himself.
CLANG!
The entire chamber shook as, at the end of it, Danzō and Sakumo's swords struck each other, followed by the old man's cane breaking apart, skidding backward while blood flowed from between his fingers. Sakumo wasn't done, already on him, continuing to attack, having Danzō try to block with the remaining, broken half of his weapon.
When Danzō staggered, losing the remainder of his ruined cane, Fugaku appeared behind him like a specter. Sensing him, Danzō immediately shut his visible eye and tried to fight blind, forming a wind-blade between his fingers and managing to cut his sleeve, but not much else. Fugaku was about to land his leg on his knee, wanting to bring him down and capture him, when he was forced to break away, as three explosive tags appeared in Danzō's hand. However... he threw them at the ceiling.
BOOM!
"He's running!" Jiraiya shouted as Danzō vanished into a hidden tunnel, Sakumo giving chase, only to be caught by Fugaku at the last moment.
"Trap!"
BOOOOOOOOM!
Just as he said it, the whole thing shook, souring Sakumo's expression.
"He's crafty; he isn't escaping upwards... He is underneath us," Ashina said at once, multiple chains stuck in the floor, holding a seal with one hand, eyes closed in focus. "There!"
Then, like a massive hand, the chains ripped apart the floor, revealing an underground chute that they all dropped down without hesitation, landing in a hidden corridor... right in front of th surprised Danzō. Still, he had some skill: he slammed Wind Release into the floor and used the blast to shoot backward, dodging... yet Fugaku's eyes found his in the process. Danzō was half a second too slow to close it, and the room had already changed for him, with Hiruzen standing before him.
"Do not presume to judge me!" The old bastard rolled as a seal activated under his wrapped face, jolting him out of it, while howling wind filled the tunnel, creating a vortex that tried to blow the group away. "Summoning—" Danzō continued, already forming the seals with the blood still flowing between his fingers.
"Don't you dare." Ashina snorted as a chain hit Danzō's wrist before his hand reached the floor, wrapping around him, while another pierced into his shoulder. The latter wasn't real... siphoning his chakra.
When Danzō felt it happen, his eyes showed fear for the first time.
"You like our seals, eh?" Ashina smiled as the wind was dying down. "Let me show you what they look like when the person using them actually understands them."
More chains erupted from the tunnel, grabbing Danzō's legs and torso, mixing both corporeal and incorporeal ones, either binding or stabbing through him. Soon, Danzō's knees hit the floor as he tried using Wind Release, Body Flicker, anything... but nothing seemed to activate. He gritted his jaw, and Ashina saw it and was able to stop him from breaking a tooth when a chain struck him in the face next, knocking a handful of teeth out.
"Seriously?" Jiraiya shrugged, grimacing.
"You think you've won?" Danzō spat blood at them, getting held up by Ashina's chains.
"Yes," Fugaku answered simply. "Exactly what is happening."
"You just lost everything..." He grunted, more blood flowing from his mouth. "The village—"
But he could say nothing more, as the chains cocooned him like a butterfly, silencing the man for good.
"Let's not give him time to do anything stupid. I'll keep him snug, nice and comfy." Ashina said with a smile, sealing the whole thing. "We still need to find and capture Orochimaru and sweep the place. I hope the others are doing just as well as we do..."