Actually, Kimimaro knew it wasn't the bloodline itself that made the Kaguya regress into the clowns they had become.
The decline had more to do with the backward "culture" they developed over time.
Based on his past-life knowledge, he theorized that the geography of the Water Country itself was the root cause.
A huge archipelago, broken into countless islands, naturally created division.
Dozens of minor lords constantly warring, shifting alliances like tides, hiring whichever mercenary clans seemed most useful at the moment.
In such an environment, long-term stability was impossible. And the Kaguya, in that chaos, rose to prominence.
But the more they were used, the more they were feared.
Civilians and nobles alike began blaming them for the endless bloodshed.
"It must be Kaguya's fault," they whispered.
That fear and resentment grew into hatred.
And in time, the clan was pushed into isolation.
The same thing happened to the Yuki and to lava and boil release clans.
Mei, in Kimimaro's memory of canon, was the last of those lines.
All of them were victims of the same negative spiral.
This environment was exactly why Kirigakure was the last of the Great Villages to be founded, and why it was usually the weakest of the five, plagued by constant internal strife.
On paper, they had excellent conditions for becoming a naval powerhouse, enjoying trade and other sea-based economic benefits.
In reality, the central Daimyō of the Water Country had the weakest control over his lords compared to any other major nation currently, since it was founded due to the ripple effect stemming from Hashirama's actions.
The only times the islands, both in shinobi and civilians, Kirigakure, and those nomadic clans, truly united were when external wars threatened them.
As soon as those world wars ended, they slipped back into civil wars and power struggles.
Kirigakure was born out of that, in symbiosis with the central Daimyō.
Hijutsu clans like the Hōzuki and Hoshigaki joined early, lending legitimacy and power.
Bloodline-based, more powerful clans like the Kaguya, though, stayed out.
Pride, arrogance, and short-sightedness made them refuse integration.
Their greatest mistake. Not that it mattered much, by that time, they were already too hated.
Even if they had tried, it was doubtful Kiri would have allowed them in.
Their joining also meant more competition for the first movers.
Meanwhile, the Daimyō's central island largest and most stable territory, contributed its strongest civilians to Kirigakure's new shinobi system.
Under the First Mizukage, Byakuren, Kiri institutionalized and scaled shinobi warfare.
He forged the Seven Swords and turned scattered killers into a professional military.
That meant even without relying on bloodline clans, Kiri steadily grew into a behemoth alongside the hijutsu clans that joined earlier.
And when the time came, they crushed the old bloodline mercenary clans one by one.
The people supported it. Civilians had long resented bloodline clans as scapegoats for the violence. They wanted peace and stability.
They didn't care who was massacred if it brought them quiet.
They even facilitated it and did it themselves whenever they could.
Haku's tragedy was proof of that.
By then, the Kaguya were completely cornered.
No noble dared hire them anymore, due to Kirigakure's pressure and their degeneration.
To survive, they turned to raids and plunder, just as Kimimaro himself had witnessed.
That only worsened their reputation.
Another turn in the negative loop.
That, Kimimaro concluded, was why they lost.
Their population was too small due to wars and isolation.
Their lifestyle was too nomadic.
It was impossible to standardize knowledge, to specialize, to civilize their shinobi arts, to grow across generations as the larger villages did.
Knowledge was their greatest weakness.
They had no writers, no archives, no scrolls, no system of written techniques.
They relied on instinct alone.
Their bloodline was powerful, but they had no idea how to refine it.
By contrast, stationary clans thrived.
This was why they also lost to non-bloodline-based "civilians" from Kirigakure so badly.
Even during the Warring States, continental clans like the Uchiha and Senju were more stable than the island mercenaries.
And the Uzumaki, settled and organized, took it even further.
They kept records, accumulated techniques, and refined them over centuries.
Their growth was exponential, while the Kaguya and Yuki stagnated.
The archipelago itself was the problem.
Island hopping, brutal mercenary work, and short-term survivalism left no room for stability.
No room for true progress.
The Yuki suffered the same fate.
Kimimaro, remembering Haku's mediocre performance, could only think of wasted potential.
That bloodline too had rotted in isolation.
And when Obito came, manipulating Kirigakure into his personal puppet, he simply massacred what remained.
Permanently weakening the Land of Water and its village.
It might have been better if Kiri had tried to assimilate and cultivate some of them instead.
But by then it was impossible. The hatred was too strong. The culture was too broken.
Kimimaro reasoned that if the Kaguya had truly been mindless berserkers from the beginning, they would never have lasted a thousand years after their Otsutsuki ancestor.
The fact that they did last proved something.
They had once been different.
Once had an order. Once knew.
But over time, they degenerated.
Trapped in a cycle.
Interbreeding without strategy.
Forgetting their own kekkei genkai and its highest form, losing the knowledge of how to use their bloodline perks effectively.
Endless island wars.
Casualties generation after generation.
Civilian hatred isolated them further.
Kiri propaganda that demonized them until they themselves became the monsters people called them.
By the time Kimimaro was born, the Kaguya were only the final stage of a centuries-long gradual decline.
A clan hollowed out by environment, culture, and history, waiting for their last massacre to put the nail in the coffin.
Kimimaro thought through all of that in silence, his mind circling the decline of his clan, the nature of the Water Country, and how history had crushed bloodlines that once stood tall.
The analysis drained him more than the physical labor of the day.
Eventually, with his body heavy and his head resting against the cold stone of the cave, he drifted into sleep.
...
The next morning, he rose early.
His breathing was calm, movements sharp, mind already reset into discipline.
He left his small camp by the riverside and made his way back toward the ruins, his steps quiet through the overgrowth.
Ashina was already there, or at least, the seal pulsed faintly, his voice echoing when Kimimaro placed his palm against the spiral crest once again.
"…So, you return. Good. I wondered if you would."
Kimimaro's emerald eyes narrowed faintly, expression unreadable. "I don't waste time."
Ashina chuckled low, the sound dry, carrying decades of bitterness.
"Then let us not waste words either."
It was the beginning of their new routine.
Kimimaro believed he already had something most shinobi children lacked: common sense paired with a broad perspective.
He had watched the whole shinobi world once before from the safety of another life, as an outsider with no stake in it.
Back then, he'd devoured the series obsessively, traced every clan's history and powers, mapped every conflict, debated every loophole on fan forums like his life depended on it.
Now, in this body, it actually did.
He understood the basics of the hidden village system, its institutions, how and why it formed, its strengths and weaknesses.
He knew what chakra was in principle, how it fueled jutsu, the different branches and types of jutsu, and how bloodlines skewed its applications.
He even grasped the factors that decided victory on the battlefield: bloodline, tactics, preparation, terrain, and information.
These were things he had once studied out of fascination, but now they became survival tools.
What he lacked was not theory, but precision.
The original world never explained the small steps.
How exactly to sense the chakra with clarity.
How to actually train Yin or Yang Release in practice, not just read about their abstractions.
That was what he needed from Ashina, the first precise, cutting steps that turned theory into power.
After all, for now, he had nothing.
No actual shinobi techniques, no research scrolls, not even scraps of written knowledge to work with.
Ashina, for his part, seemed to understand this quickly.
He didn't treat him like a normal child anymore. How could he?
The boy spoke with the weight of an adult, dissected strategy like a veteran, and his aura carried discipline most shinobi never reached, even grown.
It was strange, yes, but not incomprehensible.
This was a world where chakra itself accelerated growth, where children matured and fought fast, and where precocious talent was common.
Ashina simply judged Kimimaro as the most advanced child he had ever seen, born with both a monstrous bloodline and an unusual depth of spirit, and hardened further by cruel experiments that forced him forward even faster.
They aligned easily.
Kimimaro laid out what he already knew: chakra control and enhancement drilled into him through long isolation, sharpened further by his then-awakened talent for inward sensory perception during those long, boring meditative sessions and his sensing ability in general.
He had already internalized those distinctions that marked genin from chūnin, their fundamentals well in hand.
What he wanted now was the next step, some unique sideroads and further stamps on the main road to Jonin, like advanced nature release jutsu.
Therefore, listed his priorities plainly: sensing ability, medical ninjutsu, and broader elemental ninjutsu practice.
The Uzumaki were renowned in both sensing and medical arts, after all, and Ashina was their last library, and their clan was probably also very knowledgeable in basic nature releases, at least, since it was of that kind of renown.
Kimimaro also mentioned that on the mainland, he had already found chakra testing papers and confirmed his affinities: water and earth.
Ashina arched an invisible brow. "Two? Rare. Most shinobi carry only one."
Kimimaro said nothing, but privately, he wondered if his transmigration had tilted the odds in his favor somehow.
Still, he asked the obvious question: "Do you still have ninjutsu techniques left?"
"Of course, who do you think I am?" Ashina said, his tone edged with pride.
"Plenty. But you'll have to start small if you know what's in your best interest to establish a foundation. Affinity first. Immersion training, as our clan refined it. You'll live inside nature, learn its logic, its essence, not just recite hand seals. Then step by step, easy to hard."
Kimimaro leaned forward slightly, pressing. "So how do these affinities come about in the first place? Why water, why earth? Also, what would prevent me from 'combining' them?"
Ashina explained with the clarity of an old master. "The same way shape transformation handles size, density, and form, nature transformation handles essence. Your affinity depends on how your chakra coils and brain processes chakra as it travels after it was molded by your body and soul, and how they vibrate naturally during that process. Each person's coils resonate as strings tuned to a note, and that resonance aligns to an element."
"In nearly everyone, only one. Two is already rare. Three is rarer still, near impossible. Hand seals? They're not arbitrary gestures. They're shortcuts to trigger those pathways both in shape and nature, to force your coils and brain into specific vibrational patterns and movements before chakra exits through one of the tenketsu. Chakra is mysterious, but a programmable force after all. This is why stuff like fuinjutsu or jutsu shiki could even work."
"Water and earth in the same body is already very difficult. Your coils must learn to shift between two very different rhythms over time. To manifest both at once and get a new nature release? Even harder, and impossible for ordinary random shinobi. But exceptions do exist. But only in those elemental kekkei genkai type clans that had this engraved in their bloodline through multiple generations of hard work, initially caused by rare mutations."
"I also had two nature release affinities. But I mastered all five eventually due to my long lifespan. So, it is possible to master even outside your affinities. Just slower. Harder. With more effort and determination. But, even I couldn't combine any of them into new kinds of releases; at most I could've used some combination or fusion ninjutsu where I do multiple releases in very quick succession for more unique and powerful battlefield jutsu effects."
Kimimaro absorbed every word, but internally, his mind was already cutting the path short.
Additionally, he already knew that combining water and earth would only lead to the more mundane Mud Release from the beginning. Low-tier, ever a bit pathetic in his opinion.
Not worth years of struggle when his time was already precious. He dismissed the idea quietly right there. His goal wasn't to play with elements, too; it was to rise beyond them.