What is chakra?
First, one must extract a form of physical energy from every cell in the human body. Simply put, this relates to innate talent. The amount of physical energy a body can produce has an upper limit, and differences in talent determine how much energy a person can draw from their cells.
Next comes spiritual energy, accumulated through training and experience.
When these two energies are simultaneously extracted from within the body and refined together, they form chakra.
Shinobi normally store large amounts of chakra within their bodies. Once they begin expending chakra and need to replenish it, the body consumes stamina and vitality to restore it. For all ninja, recovering chakra is as instinctive as breathing.
Regarding physical energy: during human development—especially adolescence—physical energy surges dramatically. If a ninja possesses exceptional talent, this period (roughly ages 10 to 18) may produce so-called "monster-level" geniuses.
For example, Kakashi Hatake became a jonin at 12, and Itachi Uchiha awakened the Mangekyō Sharingan at 12.
However, the overall limit of physical energy is generally reached around age 20, when the body is fully developed. If by that point a ninja has already pushed their physical energy to its maximum yet remains only a chunin, it suggests ordinary talent. Only those with outstanding talent can potentially rise to jonin.
After 50—and especially past 60—physical decline becomes unavoidable. Even the strongest ninja will inevitably weaken with age.
Spiritual energy, on the other hand, can theoretically continue increasing as long as one maintains training. However, loss of willpower greatly affects spiritual energy. This is why Kakashi did not experience a qualitative leap in strength after the Third Great Ninja War—his emotional slump played a major role.
Thus, a powerful ninja requires:
Exceptional physical talent
Continuous training
Unyielding willpower
Only then can they maintain strong chakra.
How Are Ninjutsu Released?
After chakra is formed within the body, it must be activated through "hand seals," which act as signals or guidance to channel that chakra's energy. This entire process requires chakra control ability. The more refined and precise one's chakra control, the greater the advantage when performing ninjutsu.
For example, consider the Fire Style: Great Fireball Technique.
When Sasuke Uchiha first used it, his fireball was only the size of a basketball. When Itachi Uchiha first used it, he produced a terrifying fireball several meters in diameter.
This difference stemmed from superior chakra control. Itachi could use chakra more quickly and efficiently.
To illustrate:
A C-rank Great Fireball might require about 150 units of chakra.
Sasuke might expend over 200 units to successfully cast it, yet only achieve a basketball-sized result.
Itachi might use only 170 units but produce a massive fireball several meters wide.
Thus, when different ninja perform the same technique, the gap lies not only in "consumption," but also in "efficiency," leading to vastly different results.
Efficiency depends on:
Hand seal speed
Familiarity with the technique (training level)
Hand seal speed is straightforward—the faster the seals, the faster the technique is released.
Familiarity can be seen in techniques like the Rasengan, a no-seal jutsu.
The Fourth Hokage and Jiraiya could form it instantly with one hand. Kakashi required both hands and visible effort to stabilize it—the formation speed was not comparable. This is why, although Kakashi knew the Rasengan, he rarely used it in actual combat.
Meanwhile, Naruto Uzumaki relied on his massive Shadow Clone usage—almost like a cheat—to grind his proficiency to the limit.
This was precisely why Shimizu's Water Release techniques were so extraordinarily powerful:
He possessed a "pure water constitution" (only one chakra nature—Water), had trained relentlessly for nearly twenty years, and naturally developed superb chakra control, rapid hand seal speed, and unmatched proficiency in Water Release.
Although he later developed Fire and Lightning chakra natures, his Fire Release was only at an introductory level. His Lightning Release was somewhat better, but he had mastered only two techniques: the A-rank Lightning Release: Chidori, which he had only recently completed, and the C-rank Lightning Release: Earth Flash.
"Single-handed hand seals… I still can't figure it out…" Shimizu muttered.
He recalled the life-and-death moment from a few days ago. After using "Crescent Moon Dance" to close in on the Sand ANBU captain, Dust, his killing blow had been blocked outright. At the same time, the opponent had launched Wind Release: Wind Blade—an A-rank Wind technique.
If he hadn't instinctively abandoned his sword to form seals and unleash Chidori instead, the outcome might have been very different. If he had been able to perform Chidori with one hand back then… perhaps he would have done more than merely sever one of the man's arms—and he himself wouldn't have suffered such a near-fatal injury.
How exactly had Itachi done it?
Many plot details from his past life were fading, but Shimizu would never forget the look of sheer shock on Kakashi Hatake's face when Itachi Uchiha formed seals with a single hand.
That technique wasn't just for show. It could catch an enemy completely off guard.
Shimizu was already a master swordsman. He could attack one-handed while holding a blade, and in moments of chaos—or from a blind spot behind the opponent—he could use one-handed seals to instantly cast a jutsu and achieve a one-hit kill.
The problem was... the "God" Itachi was only a year old.
"…Sigh."
He lacked that extraordinary ninjutsu talent. Independent jutsu development and single-handed seals were his weaknesses.
Lying helplessly in his hospital bed, his entire body wrapped in bandages, Shimizu briefly felt that he might even be wrapped up more than Danzō.
Not "might."
Definitely more.
"Young man, what are you sighing for? Don't you realize you're lucky just to be alive?"
The kunoichi standing before him had long golden hair and a fiery figure—and an equally fiery temper.
She was one of the legendary Sannin—
Tsunade.
Seeing her reminded him of his earlier attempt to learn medical ninjutsu.
"…Sigh."
It was far too complicated.
To master medical ninjutsu, innate talent alone wasn't enough. First, one required extremely precise chakra control. Second, one had to study vast amounts of medical knowledge—and possess the intellect and perseverance to apply it in practice.
He had eventually given up on medical ninjutsu and instead focused on swordsmanship, the basic Three Body Techniques, and various Water Release techniques—along with Chidori, which he had only recently fully mastered.
It wasn't about right or wrong.
He had chosen his path.
He lacked the talent to become a true all-rounder. All he could do was perfect what he was capable of—
Konoha-style swordsmanship.
The Body Flicker Technique.
Water Release.
And Chidori.
"Huh?! Didn't you hear what I just said?!"
Tsunade smacked him hard on the head.
"Ow, ow, ow!"
She had not held back at all.
"Lady Tsunade, I'm still a critically injured patient…"
"If they've moved you out of intensive care, that means you're out of danger. An attack like that won't kill you."
Tsunade had absolute confidence in her medical skills.
But her next sentence made Shimizu's face change dramatically.
"At most, your wounds might reopen. Maybe get infected."
"…"
Shimizu wisely chose to shut up.
He knew she wasn't joking.
Before him stood the princess of the Senju clan—temper as explosive as her figure, strength equally overwhelming. One should never provoke her lightly.
After all, fellow Sannin Jiraiya had once had several ribs broken by her for peeping at a bathhouse—nearly ascending to heaven on the spot.
She showed no restraint whatsoever.
"That's better. You survived an S-rank mission at such a young age, and you're alive with all four limbs intact. Isn't that enough? What's with all the sighing?"
"Lady Tsunade… how are my teammates?"
Compared to reflecting on his past battle or obsessing over one-handed seals, what he truly wanted to know was the condition of his three squad members.
He had only been moved out of intensive care that afternoon, and had just regained consciousness not long ago.
So far, no one had told him what happened afterward.
"Huh? Didn't you already ask me that when you first woke up?"
"Oh! Right! You were in the ICU with me the whole time…"
Shimizu couldn't quite call it disappointment. As a qualified shinobi, he had the patience to wait for someone to come and tell him everything that happened afterward. If he had survived, then surely his teammates had too.
Of course… what he truly hoped for was that Storm Fox would come visit him personally.
Ahem. Not that only Storm Fox was acceptable. Grey Hawk and Starfire were fine too.
Maybe they'd even get emotional and hug him?
He pictured the scene in his mind and paused for a few seconds.
"…Still, Storm Fox would be better."
He made up his mind. If Storm Fox came to see him, he would finally take that step forward. At least make a start.
Who said ninja couldn't fall in love?
"I'm telling you—focus on recovery. With injuries like yours, even at best it'll take a month for the wounds to fully heal. If they reopen during that time, I can't guarantee you won't get an infection or suffer serious complications. That'll be on you."
Tsunade straightened her clothes and prepared to leave.
"I'll have the medical team help you recover as quickly as possible. And remember—don't move around recklessly for the next few days. Alright… the old man's calling me again. I can already tell he's going to make me run errands. In the middle of the night too… honestly…"
"Lady Tsunade, the Hokage has urgent business with you."
A Konoha Anbu suddenly appeared at the hospital window.
"Yeah, yeah, I'm going."
Tsunade waved impatiently and left.
But Shimizu wasn't paying attention anymore.
At the instant before Tsunade noticed the Anbu, he himself had sensed a chakra signature rapidly approaching.
That had never happened before.
Previously, his sensory ability had only been average—limited to a few meters around him. But just now, he had detected the Anbu from nearly 100 meters away without relying on sight.
Mutation?
A near-death bonus?
A transmigrator's cheat ability?
Those were minor details.
What he urgently wanted to know was his new limit.
The Anbu vanished instantly, moving at high speed toward the Hokage's office building. Shimizu focused carefully on the fading chakra signature.
He estimated that within roughly 120 meters, he could sense the presence of chakra. However, he could only gauge its general strength—not identify who it belonged to.
This ability would drastically increase his survival rate on chaotic battlefields.
In the past, he had desperately trained the Body Flicker Technique because he feared being ambushed and dying early. Otherwise, who would grind Body Flicker that obsessively?
"Ah! I forgot to thank Lady Tsunade… oh well. I'll do it after I recover."
After all, she had pulled him back from death's door. And building some rapport with one of the legendary Sannin certainly wasn't a bad thing. Basic courtesy, too.
When he had first arrived in this world, seeing all those once-famous names had made him a little excited.
Now? Completely immune.
He no longer projected personal emotions onto them.
He might know about them—but they didn't know him. They hadn't gone through life-and-death struggles together. There was no emotional foundation.
Minato Namikaze maintaining a polite distance from him was proof enough.
As for the Rasengan…
Unless something unexpected happened, that would likely remain a lifelong regret.
Itachi was only one year old now. If he wanted to learn one-handed seals, he'd have to start laying groundwork early. But Itachi's one-handed sealing appeared around Year 60 of Konoha. It was only Year 43 now—far too early. Shimizu had no idea when Itachi began developing that system.
Kakashi, on the other hand, was more reliable.
That kid was obedient—and a genius.
If cultivated properly, he could probably develop a full Chidori-based Lightning Release system ahead of schedule. And since Shimizu had played a role in its development, he himself would naturally be able to learn the derivative techniques too.
That was far more practical.
Suddenly, he froze.
A powerful chakra signature had entered his sensory range.
And in just a few breaths, it had already reached the residential building across from the hospital.