(1 year time skip)
In training ground 26, Shinra sat still on the ground with his eyes shut, implementing what he had read in the academy library a few days ago.
'Anyone can feel chakra when it is very powerful or released in large enough quantities, however that would only be the case in a combat situation.'
'In a battlefield, the enemy won't be foolish enough to flex his chakra whilst hiding. If I could sense their position and strength from far away, I could make a better judgement on whether to escape or not.'
The scroll mentioned that although there are many different sensory techniques—some even defined as a kekkei genkai—all of them essentially follow the same concept:
Refining chakra and changing its properties to focus on perception, essentially entering a sensory mode. To extend the range of perception, the ninja can select a medium to spread his chakra through; it could be earth, water, or even webs like Kidomaru's.
Shinra exhaled softly and began to concentrate. It was surprisingly smooth to change his chakra to sensory chakra; now all that was left was projecting his chakra outward.
He released the chakra around him into a sphere shape with him at the center. Around him, a large sphere seemed to be surrounding the entire training field.
'Hmm? What is going on? Why does it span over a kilometer even in a condensed form? According to the scroll, only advanced sensors can detect from over kilometers away.'
Shinra ran through quite a few possibilities from the anime, but most of them were improbable. So now he could only chalk it up to having a talent in sensory perception.
'I originally thought that having a sphere shape without a medium would generate an area where I can sense with better clarity, but it only showed signs of the shape being distorted after a kilometre.'
'I wonder how much I could cover if I used the earth as a medium… let's try it out.'
Shinra stopped his sensory technique and crouched down with his hands touching the surface of the ground. 'Since I will be using the earth as a medium, I shouldn't need to worry about maintaining the shape of the field.'
…..
Inside the Hokage building, Hiruzen sat on his chair with piles of paper lying on his desk. The situation with the Uchiha clan kept getting worse as time went by. Though two years ago he'd allowed Uchiha Itachi to graduate early, it was for two reasons:
The first was to boost the ground-level reputation of the Uchiha clan, and the second was that Itachi was most likely going to be the next clan leader. With his way of thinking, it was very likely he would be able to handle the growing dissatisfaction of the Uchiha clan with the village.
"I haven't paid Naruto a visit in a while, he should be two years old right now."
'Anything to get me away from these papers for a while.'
Whilst walking down the streets of Konoha in a disguise, Hiruzen reached the house of Naruto Uzumaki.
Although an orphan and alone, Naruto wouldn't be allowed to enter an orphanage since the Nine Tails inside of him might try to take over. Hiruzen comes by every few weeks to check on the seal. He has appointed an ANBU squad to guard him and ANBU personnel to take care of him until he is three.
'Now that he is a little bigger, he really does resemble Minato quite a bit— hmm?'
The sensation of someone spying on him caused Hiruzen to stop in his tracks. 'Spies or Root?'
Hiruzen locked onto the chakra signature and used his own sensory technique, though before he could get more than a dozen kilometers, the chakra field suddenly vanished.
"'Dog,' lead a team and track down the person who just released that chakra field."
"Yes." A voice said from behind and the figure disappeared.
"'Weasel,' look for Kobayashi Ginro and tell him to inspect the seals in this house and to fix them up."
'Naruto's house should be engraved with the same seals as a clan leader's—seals that prevent anti-spying. The most likely person who could've tampered with them is… Danzo.'
Dozens of other jounins felt someone trying to sense their positions. Though they were used to it in the battlefield, in the place where they were supposed to relax, having that feeling was uncomfortable.
It was like having someone try to open the door to your house in the middle of the night.
Though the culprit of this incident was sprawled on the ground unconscious.
….
(A minute ago)
The moment Shinra let his chakra sink into the earth, everything went wrong.
The earth didn't offer any resistance to his chakra and in fact seemed to conduct it quite easily.
All of a sudden, thousands of lifeform signatures appeared in his field, from small lifeforms like animals and insects to humans. His mind wasn't able to withstand the pressure exerted on it.
His breath hitched.
'I must stop this.'
The range kept expanding despite his increasing mind-splitting headache. Twelve kilometres—but distance didn't matter anymore. It was like trying to listen to a thousand conversations at once.
Pain laced through his skull.
His vision blurred, blood seeped from his nose.
To make it even worse, he felt a huge chakra signature unlike anything he had felt before.
"Shit—"
The thought never finished.
Shinra's hands slipped from the ground as his body gave out, his mind went blank under the strain. The sensory field collapsed as if it had never existed.
He hit the dirt without even realizing he was falling.
Shortly after he passed out, five masked figures surrounded his body.
"Is this him, captain?" A slender figure asked the captain with white hair.
"The chakra signature matches, though it is quite surprising he looks to be an academy student," Dog said, his voice tinged with slight annoyance.
"He probably was unable to withstand the mental burden from the attempt, though it doesn't take away from his talent at all. A twelve kilometer radius at his age is unheard of. He might be as talented as that Uchiha kid who graduated two years ago," Eagle said as he checked Shinra's vitals.
"Cat, take him away to the hospital and watch over him. Eagle, check the area and look for any other chakra signatures," Dog said as he flickered away to report back the info he had gathered.
Back within the Hokage's office, Kakashi reported what had happened to the Third Hokage.
Hiruzen released a puff of smoke from his mouth. 'An academy kid with an absurdly high talent in sensory capabilities. Usually sensory techniques are heavily dependent on mental energy for control.'
He waited for a few minutes before Eagle delivered a file that contained Shinra's information.
'Kamikaze Shinra, 7 years old, orphaned, both parents killed in the Nine Tails attack, Class 2-B, usually silent in class but seems to spend most of his time training and in his spare time heads to Konoha's square to help elderly people.' As Hiruzen read the report, a small smile crept onto his face.
'What a good seedling.'
————
A/N:
The process of sensory techniques is not covered heavily in the manga and anime, so I added a bit of my own touch into it.