Sasuke lay in bed, staring up at the ceiling, stomach full from Kakashi's good home-cooked dinner, something Sasuke hadn't had a home-cooked meal since his mother, his cooking… well, it was best not to talk about his skills in that area. The only area Sasuke was somewhat confident in was grilling fish.
'It wasn't bad.'
Sasuke scoffed at his own thoughts before turning over in the bed and closing his eyes, falling asleep faster than he normally would for some reason.
Kakashi silently cleaned the kitchen, scrubbing plates, rinsing glasses with soapy water, and drying everything before putting it away in the cabinet.
'For someone so reluctant, he sure did fall asleep fast.'
Kakashi smiled softly, walking outside and locking onto the chakra signature he was looking for before body flickering.
- Morning -
Waking up, Sasuke rolled out of bed and walked into the living room, not seeing Kakashi there, he knocked on Kakashi's door, sliding it open when he didn't get an answer.
'Not here either.'
Sasuke turned, going outside, blinking in surprise at the new addition of doors in the ground.
Opening the two doors, Sasuke peered down at the wooden stairs leading to a wooden hallway, candles lining it.
Walking the 12 stairs, Sasuke continued down the hallway, hearing voices as he drew near a closed door at the end of the hallway. Opening the door, Sasuke watched as Kakashi directed an anbu with a motion, the anbu weaving seals and creating…
'Wood release? A Senju?'
Sasuke's eyes widened as he watched the anbu create a large table, the 50x50 room as big as a large full-sized house, decorated for what seemed to be various things, piles of materials, some Sasuke recognized and some that he didn't.
"Sensei, what is this?"
Kakashi hummed.
"A room where I can be creative."
Kakashi replied simply, walking around and laying seals at various points in the room. The whole room was a fuinjutsu feedback loop of chakra-absorption seals that absorb any stray jutsu or chakra that hits the walls and channel it through a series of conduction seals to power the chakra detection seals and fuinjutsu he had secretly been working on to keep out two individuals. These two seals were a Spatial Anchor Matrix and an Ironclad Seal.
The Spatial Anchor seal is triggered when someone attempts to phase through the wall (like Kamui's intangibility) or teleport inside (like Flying Raijin). The anchor script detects the spatial distortion. It uses the room's stored chakra to forcefully stabilize the coordinates. This makes the physical matter of the walls completely absolute, forcing the intruder to materialize outside the wall or causing the teleportation formula to fail entirely.
The Ironclad seal, on the other hand, remains invisible unless triggered. The moment the seal is triggered, the kanji glow and physically harden the atomic density of the room's materials. If an enemy tries to force their way in, the absorption seals will feed on the chakra they use, instantly boosting the room's physical durability and spatial locking power to match the attempt.
Kakashi worked for 20 minutes, going over each line multiple times for the walls before linking the seals into the floor and ceiling as well.
Once done, Kakashi pointed to the wall on the opposite side.
"Hit it with Chidori."
"Are you sure?"
Sasuke had watched Kakashi work, layering each seal in a clearly organized way, not understanding any of it, but having no desire to destroy or damage it.
Standing there silently with his anbu mask on, Yamato wondered if he was insane.
'We're underground, does he want to bury us?"
"If you damage it, even a scratch, I'll give you an S-Rank Lightning jutsu."
Kakashi laid the bait and had to suppress a smirk as any hesitation on Sasuke's face vanished, and he turned to flash through the seals, chidori chirping to life on his hand, purposefully charging as much chakra as safely possible into it.
"Kakashi."
Yamato shifted towards the entrance, ready for the whole underground room to collapse.
"Relax."
"It's kind of hard to relax when I'm about to be buried alive."
Yamato relented upon seeing Kakashi's confident face, but he kept his hands ready and out of his pockets to perform the wood locking wall jutsu just in case.
"Don't, the jutsu would crumble, and the chakra used to create it would be absorbed."
Kakashi warned Yamato before Sasuke threw his arm back, taking off in a run, Sasuke not noticing that the floor was actively absorbing his chakra when the chidori hit the ground.
In the short time it took Sasuke to cross the distance to the wall, the chidori in his hand was already at a quarter of its original strength when he thrusted it at the wall.
Kakashi watched as the seals worked as intended, chakra was drained, and the wooden walls were reinforced, withstanding it without so much as a scratch.
'Hehe'
Kakashi was excited that this part of his seals was moving correctly, though he did not wish to attempt breaking into it himself; the seals would either fry at the chakra absorbed or kill him first, depending on how much they could actively absorb.
Sasuke stared at the wooden wall in a daze before looking back over his shoulder at Kakashi.
"What did you do with those seals?"
Sasuke wasn't particularly interested in seals beyond the basics, not because he looked down on them, but because he didn't feel they were particularly for him.
"The entrance will be even more complicated."
Kakashi replied before working on something in the room.
Sasuke watched, only realizing that the podium thing near the door was somehow connected to the entrance doors. The more Sasuke watched, the more his head spun at the connections, the way some seals seemed to be for one purpose, like a sort of layered defense that was beyond his basic understanding of seals. To Sasuke, it looked like another language with the most confusing grammar in the world.
Yamato was in the same boat as Sasuke; his own knowledge of fuinjutsu was intermediate at best, and even he could only understand the more basic ones, like the detection seals at the entrance, before they sank into the wooden walls, and the paralysis seals, which sank into the floor, walls, and ceiling as well.
'What the hell does he plan on making in here that he needs this many complicated seals?'
Kakashi worked and worked, brush flowing from seal to seal, connecting them in place and applying more seals to hide them after checking if everything was working correctly.
With that done, Kakashi walked up the stairs and outside, working on more seals as he called out Yamato.
"Hey, I need you to make one more thing for me, then I'm done, I promise."
Kakashi clasped his hands together, Yamato ultimately giving in.
"What is it that you want me to make? My chakra is sort of running low here, Kakashi."
Kakashi sheepishly rubbed his head.
"Aha… Well, I'd simply like two podiums like the one inside the room. I'm going to connect them with the one inside the room."
Yamato created the two podiums, feeling exhausted.
"There, I can't make more, for the love of the Will of Fire, don't ask me to make anything else."
Kakashi nodded, feeling a bit bad about dragging Yamato here to build this all night and into the morning. Even if he promised to pay him, it was still a bit much to ask of someone. Kakashi unsealed a large sum of cash, enough for Yamato to take a long vacation if he weren't an active ninja.
"Here, you've helped me a lot today. I really appreciate it."
Kakashi observed his exhaustion, even the mask failed to hide it.
"Let me help you home."
Before Yamato could refuse, Kakashi clasped a hand on his shoulder and vanished just as Sasuke walked back up.
Kakashi returned a few moments later and began the more intricate work on the podiums, connecting them to the one inside the underground room using converting seals and other methods.
Placing his hand on the podium to the right of the doors, Kakashi traced the outline of his hand with his brush, letting the ink dry, then did the same with the other.
Sasuke no longer wished to watch; he felt his brain would melt and drain from his ears if he attempted to understand this madness, so he walked away to practice something much simpler, like kenjutsu or shirukenjutsu.
Kakashi hummed, finishing everything an hour later, sighing as it was a lot of working, some fine tuning, but it was worth it, looking at the entrace and walking up to the podium, pricking his thumbs and rubbing it on the podium to the right, the blood absorbing into the wood and the carved symbols along the length of the podium glowed a soft blue before fading.
"I did it."
Kakashi smiled like a madman, inspired by the Inventor reward he got for bringing a train to Konoha much earlier than canon.
- Chapter End -
I'll leave the descriptions of what the fuinjutsu is that Sasuke and Yamato couldn't seem to understand.
Blood-Key Signature Podium
The Mechanic: The podium on the right side of the door requires a blood signature. Authorized users must smear a drop of their blood onto it. The seal instantly reads the unique genetic and chakra signature within the blood. If it matches the registry, the Directional Valve momentarily parts, allowing a normal, unhindered entry.
Silent Phantom Beacon
* The Mechanic: Microscopic, invisible scripts woven into the door frame. If someone phases through using Kamui, emerges from the floor via Mayfly(Black Zetsu), or forces the door open without a valid Blood-Key, this seal triggers silently.
* The Connection to Kakashi: It transmits a localized chakra pulse keyed directly to a matching reception tag tattooed or carried on Kakashi's person (similar to how Minato feels his Flying Raijin kunai). It provides an instantaneous, silent mental alert that an unauthorized entity has breached the room.
Latent Neuro-Static Grid
The Mechanic: This seal lies flat and completely dormant on the floor just past the threshold. It intentionally allows Obito or Black Zetsu to fully enter and "relax" their techniques, assuming they slipped past the outer defenses.
The Trigger: The moment their physical body completely materializes and touches the floor, a massive surge of paralyzing lightning-style chakra shoots upward.
The Purpose: This won't permanently break the high-level techniques, but the sudden, unexpected physical shock is designed to force a brief moment of hesitation or physical lockup. This momentary lapse in focus prevents them from immediately reacting to the main trap.
Vampiric Lockdown Circuit
The Trigger: Activated simultaneously with the Paralysis Grid, the room shifts from "Stealth Mode" into "Execution Mode."
The Primary Aggression Seals: Heavy, thick script bands shoot out from the walls, physically binding the intruder's limbs.
The Advanced Siphon Loop: This secondary layer of the Chakra Siphon Grid targets the intruder directly. If Black Zetsu or Obito tries to use their chakra to break the physical bindings or phase away, the seals violently tear the chakra directly out of their bodies.
Feeding the Ironclad Seal: This stolen enemy chakra is immediately funneled straight into the Ironclad Reinforcement Formula.
- Non-trap seals below -
Chakra Resonance Doorbell
* The Mechanic: A specific, glowing handprint script placed on the outer door. If a guest (like a messenger or an ally without a registered blood seal) places their hand on it, the seal gently pulses.
* The Kakashi Console: Inside the room, a master seal on the podium will light up and hum in response. If Kakashi is inside, he can place his hand on the master seal and channel a brief spark of his own chakra. This sends a release command via the Conduit Scripts, temporarily disarming the door's physical locks so the guest can walk in safely.
(This involves the left podium at the entrance, unauthorized people that Kakashi can let in or ignore. The right is for the ones allowed inside without issue.)
Signature Discriminator Seal
* The Mechanic: This acts as the brain of the security loop. It monitors the exact wavelength of energy passing through the walls or floor during a breach.
- For normal threats that don't have space/time techniques or something along the lines of Zetsu's technique-
The Ordinary Intruder
* The Action: A rogue ninja tries to pick the lock, smash the door down, or slip inside using basic stealth.
* The Room's Response: The Signature Discriminator recognizes that no space-time folding or wood/earth merging is occurring. It keeps the heavy Chakra Siphon Grid and Vampiric Lockdown completely dormant. Instead, it only triggers the Latent Neuro-Static Grid. The fool steps inside and is instantly paralyzed, flat on the floor, perfectly preserved for Kakashi to interrogate later without the room breaking a sweat.
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That's all, my brain hurts. Hope you enjoy the chapter. I'm planning on making Kakashi the Tobirama of this generation, with not just ninja inventions, but so, so much more.