Every human in this world carried a baseline chakra inside their coils.
It was like having an extra circulatory system woven through the body, constantly feeding into strength, stamina, and resilience.
This alone meant that even ordinary people here were stronger, durable, faster, had better reflexes, processing speeds, and more enduring than anyone in Ryusei's previous world.
But there was also a danger: if you exhausted yourself so completely that no chakra remained passively circulating, your body, so used to operating with it, could collapse and even die.
Chakra itself came from two roots: physical energy and spiritual energy.
Physical energy was drawn from the body cells, nutrition, and natural vitality.
Spiritual energy came from the mind, willpower, memory, experiences, and growth.
Together they created chakra, a unique phenomenon of this world… or perhaps of this entire dimension.
After all, this was also a place where natural energy flowed through the land, souls, and a 'Pure Land' dimension solely for souls, existed, and reality itself could be bent by the mathematical-like laws of jutsu-shiki.
Chakra was the cornerstone that tied all of these mysteries together.
Hagoromo Ōtsutsuki hadn't given chakra to humanity; he had simply taught them how to mold it because he was born with it and had a better understanding of it.
His descendants, and Hamura's, carried natural advantages not only from him but from the alien Ōtsutsuki lineage itself, traces of chakra fruits devoured in the past, with the most potent source being Earth's own God Tree.
Clans like the Senju, Uchiha, Hyūga, and Uzumaki, and perhaps Toneri's clan and Kaguya Clan, were born with that inheritance already in their blood.
When shinobi spoke of "chakra control," they usually meant the ability to use the right amount of chakra for a technique, neither too much nor too little, just enough to achieve the intended effect without error and without harming themselves, or being too wasteful.
Beyond that came nature transformation, shaping the chakra so it behaved and vibrated like an element: fire's combustion, wind's sharpness, lightning's piercing, water's flow, earth's solidity.
Shape transformation came next, molding chakra's form, density, speed, visibility, and precision into weapons, barriers, or constructs. And there were further layers still: chakra channeling, distribution, amplification.
Each shinobi's coils and brain naturally leaned toward one or more affinities, behaving "as if" their chakra wanted to become fire, or wind, or some other element.
That gave them shortcuts, a head start compared to forcing an unfamiliar affinity.
But Yin and Yang Release were different. Few ordinary shinobi even knew of them, let alone trained them.
They existed below the elemental transformations, tied directly to the chakra's root: the balance of spiritual and physical energy itself.
Yin represented a chakra richer in spiritual force, thought, imagination, and will.
Yang represented a chakra richer in vitality, the body, biology, and life force.
Together, they defined the very foundation of chakra before it took on any elemental form at the expelling stage at one chosen tenketsu point.
And depending on the ratio used between the opposites, Yang and Yin Releases are created.
Combat levels in this world followed a rough ladder of expectations. Before a child could even join the Academy, they had to demonstrate baseline shinobi potential.
This was tested through chakra sensitivity screenings. At that age, molding and control were usually impossible, so it was more about instinct and how naturally their chakra responded.
Alongside this came checks for physical aptitude, cognitive and mental sharpness, and most importantly, obedience.
These were carried out through a mixture of medical examination, sensory evaluation, and, in some cases, direct Byakugan observation.
Graduation to the rank of genin required far more. Every student had to master the Three Academy Jutsu, basic weapon handling, hand-to-hand combat drills, and teamwork coordination.
They were also tested on loyalty, shinobi theoretical knowledge, and strategy. Identifying and dispelling simple genjutsu was mandatory, as was demonstrating the ability to channel and mold chakra into usable density and size, though still only at a basic level.
Exceptions were possible for unique talents: even without a ninjutsu skill, a prodigy in taijutsu could graduate, as shown by the likes of Guy and Lee.
In the end, graduation was determined by an aggregate of scores across many factors, weighted differently depending on the Academy's priorities at the time.
The leap from genin to chūnin required much more than theory. At this stage, a shinobi was expected to apply chakra reinforcement consistently to at least one part of the body in live combat.
A common example was using Body Flicker techniques to explosively enhance speed, or focusing chakra into fists and legs for reinforced strikes.
Some developed defensive reinforcement, trading mobility for durability.
Intermediate control exercises, tree climbing, water walking, and basic shape transformation drills were standard training at this level.
Tactically, chūnin candidates were tested on leadership under pressure, usually through the Exams or equivalent life-threatening missions.
This was also the point where specialization began, with each shinobi focusing their growth into one or two fields: taijutsu, elemental ninjutsu, weapons, stealth, or other combat styles.
From chūnin to jōnin, the requirements became steeper. A jōnin was expected to master full-body chakra enhancement, able to reinforce arms, legs, core, and defensive layers all at once in battle.
Their speed typically matched or exceeded the sustained Body Flicker level, maintained without collapsing under the strain.
Some jōnin further proved their conditioning by unlocking one or two of the Eight Gates, though this was not mandatory.
Beyond raw ability, a hallmark of the jōnin rank was the creation or mastery of an A-rank technique or more.
This might be an original technique of their own design or the perfected use of an advanced elemental jutsu.
Just as important was experience: no shinobi could be trusted with the rank of jōnin without a proven record of leadership and survival in high-risk missions where lives were truly at stake.
Kage stood apart from even this level. Reaching that height required overwhelming influence and support within the village as much as it required personal strength.
While most Kage had one or more S-rank techniques, or combat abilities so overwhelming they bordered on it, the real requirement was the ability to stand at the center of the village's power, both politically and militarily.
However, ranks never matched actual strength perfectly. There was always a wide margin of error, and the so-called "hallmarks" of each stage were hardly absolute.
For example, the original Ryusei was officially only a genin, yet he had already mastered all the chakra control exercises expected of a chūnin.
More than that, he had achieved chakra enhancement on a level comparable to a jōnin.
The only reason it didn't show in full was his age. His young body couldn't maintain that enhancement for long, unlike, say, a thirty-five-year-old civilian-born jōnin in their prime, whose baseline physique would simply last longer even with a weaker bloodline.
What allowed Ryusei to reach that level so early was a mix of Senju talent and inherited shortcuts. His father had left behind guidance that accelerated his growth, and his bloodline itself gave him an edge.
The Senju body was naturally better attuned to chakra, with denser and more widely spread coils than ordinary shinobi. Because of this, chakra enhancement came to him more easily than it would to most.
Ryusei's baseline chakra control was already above that of most chūnin, largely because he had been immersed in medical practice from a young age.
Medical ninjutsu demanded constant precision, so he had trained endlessly with advanced control exercises just to reach competence.
For that reason, the current Ryusei felt there wasn't much room for further dramatic improvement in this area, aside from what he was already planning through his shortcut toward nature transformation.
Even before mastering elemental releases, he could simulate their qualities during control drills. For example, sharpening the chakra to mimic wind, heating it to imitate fire, or condensing it into density like earth.
These exercises built elemental affinity early, making later mastery easier.
To support this, he intended to practice immersion and observation of the natural elements themselves, through meditation, visualization, and breathwork, cultivating an instinctive connection to how each element behaved.
Ordinary nature releases might not sound as glamorous as legendary bloodline powers, but who said Ryusei couldn't combine them into devastating results?
Hiruzen had shown what was possible with mastery of all five.
With enough creativity, Ryusei could one day push beyond, developing new elemental combination jutsus or even entirely new 'elemental kekkei genkai'.
That was a distant goal, however. For now, he kept his focus grounded, refining the simple exercises in front of him, and making sure he could do them better than anyone else.
The Senju had long been called the "clan of a thousand skills," and Ryusei finally understood why after transmigrating here.
It was because they could perform the most different releases individually as a clan. After all, their bloodline granted them unusually flexible chakra coils.
This flexibility made it easier for their chakra to shift micro-patterns and behaviors, creating the subtle "vibrations" needed for new elemental releases.
It also allowed them to hold and switch between multiple natures, even contradictory ones, within the same arsenal, or sometimes even within the same technique.
Ryusei recognized this as a massive advantage.
On top of that, he wasn't just Senju; he was also a transmigrator, carrying two souls' worth of spiritual energy.
That meant his chakra control could reach levels closer to the Uchiha's famed precision.
And if Senju adaptability combined with Uchiha-like control, the result would be terrifying: a true multitasker of chakra natures, capable of pushing beyond even the old legends.
To Ryusei, it felt almost like a divine mandate. The path ahead was clear; this was the road he was meant to walk next, initially at least.
He sat cross-legged on his bed, eyes closed, breath steady.
The neat little protocol he'd mapped out on the road back to Konoha replayed in his mind: meditation for calm, crude internal perception, where his sensory talent gave him an edge, and steady refinement of his coils.
On paper, it looked flawless.
In practice? Much tougher than he expected.
"Tch. If only I had a Byakugan," he thought, irritation gnawing at the edge of his focus.
"Real-time, fully direct observation and feedback of my chakra coils instead of fumbling around with this makeshift sensing? That'd be perfect."
A pause.
"…Wait. Who says I can't? Byakugan - it's mine the moment I decide to take it. Borrowed, permanently. Secretly, of course."
A grin cracked through his calm. "Finders keepers, losers eyeless."
The thought only spiraled from there.
"Main Branch calls it bloodline destiny. But if I rip your destiny out of your head and stick it into mine, isn't it mine now? Sounds fair. I call it redistributing fate."
Another grin. "Winner takes all. The Hyūga hoard their eyes like treasure, but treasure's only worth something when somebody else steals it."
His breathing stayed steady, but the greed boiled under his skin, a predator crouching behind calm eyelids.
"Better pray you're not stupid enough to show up on the battlefield where I'm hunting, because if you do… well, don't worry. I'll make good use of what you leave behind."
He had already made some plans in the next instant and calculated everything related.
The Main Branch was the only realistic source of Byakugan possible to tap into, and the only world where such a chance would exist was the upcoming war.
In that chaos, with bodies falling by the thousands, who would notice if a pair of pale eyes went missing?
As to whom he would take it from, well, whoever was closest to his hands.
'Hiruzen, Hiruzen… hopefully you press them hard enough, and they're arrogant enough to agree..." Ryusei mused.
The Main Branch was the Hyūga's best fighters, and unlike the Side Branch, they had always managed to stay out of the meat grinder in past wars.
Whether they could be forced onto the battlefield this time was uncertain, but this war promised to be different on many levels.