Chapter 31: How Can You Possibly Sleep at Your Age?
"Done."
Hiiro Rinko exhaled a long breath and laid down the final rune on the scroll, declaring the Storage Scroll complete.
Unlike standard Sealing Jutsu (Fūinjutsu) used to seal other objects, applying Fūinjutsu to a Storage Scroll is much more difficult because it involves the application of Space-Time Ninjutsu (Jikūkan Ninjutsu).
If the sealing formula reacts with the Jikūkan Ninjutsu embedded in the scroll during the drawing process, it can easily cause the entire scroll to be destroyed.
It's similar to how a person being sealed will resist, or how genjutsu will fail if the target's Chakra disrupts it. In essence, it's a conflict between Chakra signatures.
To open a larger storage subspace, a more complex Space-Time Ninjutsu is required, which in turn makes it more difficult to draw the sealing formula without interfering with the existing traces.
This is why the price of a Storage Scroll is directly proportional to the size of its subspace, and inversely proportional to the physical size of the scroll itself.
And it's worth noting: you must never place a Storage Scroll inside another Storage Scroll.
The subspace created in paper or cloth by Jikūkan Ninjutsu is not that stable. Even with the constraints of Fūinjutsu, stacking multiple subspaces has a high probability of causing a collapse, which would nullify the scroll's preservation effect.
The contents could be scattered across time, damaged by spatial distortion, or simply drift into another dimension entirely... Having it just explode on the spot is actually the best-case scenario.
The Storage Scroll Rinko had just completed had a capacity of about one-quarter of this study room, roughly thirty-six cubic meters. After leaving a margin for error, the usable capacity was around thirty-four cubic meters.
It wasn't an exceptionally large space for a scroll of this size, but it was more than enough for the three of them.
Yes, although he said they needed to show the school some results, Rinko had no intention of handing this scroll over—at least, not yet.
This study room had been assigned to the three of them as their personal activity room for their school life. That being the case, they had to furnish it properly.
Study materials like bookshelves, a blackboard, and desks went without saying, but training equipment and a rest area were also necessary. Therefore, all the miscellaneous items that were used often but were hard to store would be stuffed into this scroll, which would then be hung on the wall.
After all, inside the scroll, they didn't need to worry about organization. The spatial efficiency was far greater than the classroom's.
"Subspace structure... normal. Storage function... operating normally. Fūinjutsu is stable. A very successful attempt."
Rinko casually stuffed the pen he'd used to draw the runes into the scroll and pulled it back out, shaking his head in delight. It wasn't smugness, but the pure joy of having mastered a new technique.
"So we can put all that stuff inside now, right?"
Karura, who was hugging his left arm, looked up and pointed to the pile in the corner by the window. Besides training equipment like weight blocks and dumbbells, there was a heap of miscellaneous junk: Rinko's tools and parts that the girls couldn't understand, Karura's Medical Ninjutsu notes, various ingredients for mixing medicines...
There was even an anatomical model, which Rinko used as a teaching aid when instructing the girls in taijutsu.
Once all that stuff was packed into the scroll, the entire study room would feel much more spacious.
"Mhm. First, I'll teach you two how to unseal this scroll."
Pulling his arm free from Karura's grasp, Rinko clapped his hands to get the girls' attention.
"As a basic, reusable sealing jutsu, the principle is just like using a key in a mechanical lock. You inject Chakra here, and then unlock it by following a set sequence."
After storing the pile of junk, he pulled out a folding table near the window and placed the scroll and two water cups on it.
"Want to try?"
"Okay~"
"Oh, coming."
Karura and Pakura came to his side and, following his instructions, tried to send the water cups into the scroll.
As expected, Karura did it easily, but Pakura's attempt wasn't as smooth.
"You need to be faster when you make the turn at this point."
Rinko, who looked like he'd been expecting this, took Pakura's hand from behind and guided her as she injected Chakra to unlock the seal.
"M... I know."
Being in such an intimate position with Rinko was a bit much for Pakura. Her face instantly flushed red, but she followed his guidance and began a new attempt.
Although her Chakra control was already much better than before thanks to their guidance, the habits she had built up since she started learning were not so easy to correct.
Because she lacked confidence in her control, she was always overly cautious when injecting Chakra. This made her Chakra speed too slow to meet the requirement, failing to unlock the seal.
"This is also a very common anti-decryption method used to protect valuable property with Fūinjutsu. It's often paired with various self-destruct formulas to lock down a vault. ...Mhm, you don't need to memorize this. It's not commonly used, and it won't be on the test."
Hearing this, Pakura obediently nodded.
On the other side, Karura's attention had instead fallen on Pakura, whose hand was being held from behind by Rinko.
What the! How is that any different from a hug!
Protesting silently in her heart, the cute little rabbit puffed up her cheeks and started to whine at Rinko.
"Heeeey, Rinko~ I didn't learn how, either~ Waaah!"
"Stop messing around."
Rinko curled two fingers and tapped Karura lightly on the head as a 'punishment,' his eyes narrowing slightly. "If I recall, little rabbit, don't you still owe me an analysis report on the 'Tenketsu Unblocking Jutsu'?"
"I'm writing it, I'm writing it~ But a two-thousand-word jutsu analysis is just too haaard~"
Karura clutched her head and crouched down, her voice a small, whining complaint.
I can't finish it! There's no way!
Compared to ninjutsu for killing, Medical Ninjutsu for saving lives required far more absolute precision. An assignment on it was naturally more brain-draining.
She was only six years old!
Learning the basics of Medical Ninjutsu was one thing, but who makes a kid this young write a full analysis of a jutsu?!
"You're a demon! Rinko is a mean, mean demon!"
Pouting, Karura looked up at him, her eyes brimming with tears.
"Hah… I guess you have a point."
Feeling he had gone a bit too far, Rinko scratched his fluffy red hair and then made Karura a very tempting offer. "One thousand... no, eight hundred words will be fine. If you can write it, I'll give you a reward. How about it?"
"Really?"
"Mhm."
"Yay!"
The girl called 'little rabbit' really did hop up just like one.