After eating his fill, Umino Yoru excused himself and returned to the underground lab.
Fortunately, Aburame Shibi was tactful—or perhaps his scouting range was limited—as he only deployed his kikaichū around the perimeter of their defense zone, not bothering to monitor the four of them. Otherwise, slipping away would've been difficult.
Once in the lab, Yoru eagerly unsealed the storage scroll and began setting up the experimental equipment. The delicate instruments took him two full days to install properly.
With the lab finally operational, his first order of business was dissecting the bisected Water Bat summon, preserved in saline solution.
The results were promising—but also frustrating.
The good news: After days of research, he'd successfully decoded the bat's ultrasonic principles.
The bad news: While chakra was versatile, it still obeyed the law of energy conservation. Replicating the bat's precise biological mechanisms required enormous chakra reserves and exquisite control.
Beyond a 3-kilometer detection range, the chakra cost and control demands increased exponentially.
For practical combat use—like the Byakugan's real-time tracking—the Sonic Radar Technique worked best within 200 meters.
Further optimization could expand the range without increasing chakra consumption, but diminishing returns were inevitable. Unless he made a breakthrough in chakra control or transformation techniques, progress would stagnate.
"At this point, the research isn't worth the effort."
Yoru frowned. While not a dead end, the input-output ratio had become untenable.
But just as he was about to shelve the project, a serendipitous discovery reignited his enthusiasm.
While cross-referencing summoning research, he stumbled upon an obscure study—tiger-type summons.
Most institutions studied them for their combat prowess, ranking them alongside raptor-type summons as premium research subjects.
But buried in the data was an overlooked observation:
A tiger's roar carried a hypnotic震慑 effect, audible for miles—even capable of inducing cardiac arrest in ordinary creatures.
"In other words… tiger roars have extreme penetration and range."
A realization struck him like lightning.
The Science of Sound
From his past life's knowledge, humans hear frequencies between 20 Hz to 20,000 Hz.
Infrasound (below 20 Hz) Ultrasound (above 20,000 Hz)
Tiger roars fell into the **infrasonic range (14-18 Hz)**—explaining their bone-shaking resonance and long-distance propagation.
Studies showed these low-frequency waves could:
Penetrate skulls, disrupting brainwaves (causing dizziness/numbness). Trigger heart failure in small animals. Even predict earthquakes (tigers sense seismic infrasound).
"A tiger's roar isinfrasoundenhanced by chakra!"
In the ninja world, summons amplified these effects. Their "illusion-like威慑" was likely chakra-boosted infrasound—far deadlier than natural roars.
A New Direction
Fortunately, his Water Bat research provided a foundation. Without it, procuring a tiger summon for study would've bankrupted him.
Now, armed with data and experience, he dove into Infrasonic Radar development.
For weeks, he split time between:
Lab research (when off-duty). Field testing (during patrols, discreetly reading scrolls).
Field Test: Fishing with Infrasound
"That's enough for today."
Yoru archived his notes and hurried back to the patrol outpost.
"Captain, were you 'relaxing' at the merchant camp again?"
Shukudō smirked, sniffing the air—only to recoil at the stench of disinfectant.
Yoru tossed him a vial of Water Bat No. 6.
"Keep quiet if you want more of these 'little darlings.'"
"Yes, sir! Lips sealed!"
Shukudō cradled the poison like a cherished lover.
Meanwhile:
Inuzuka Ryō and Kosugi prepared dinner. Yoru "fished"—now the only one who could catch Golden Luo Fish (thanks to overfishing).
Standing on the river, Yoru formed the Tiger Seal.
"Infrasonic Radar Technique."
A pulse of undetectable sound shot toward the depths. Moments later—dozens of fish floated belly-up, including several Golden Luo Fish.
"Perfect."