Spiritual energy was the other half.
If physical energy was, in the simplest terms, the power produced by the body, then spiritual energy was the sheer power of the soul.
And that was where the Uchiha truly excelled.
It was the foundation of their so-called Sage Eyes inheritance.
The Sharingan was only the most obvious expression of it.
The whole package was broader.
The dōjutsu itself.
Its potential evolution.
An unusually strong affinity for Yin Release, most famously expressed through genjutsu.
But also less celebrated advantages.
Chakra control.
Shape transformation.
Channeling.
The ability to manipulate complex techniques with unusual precision.
And perhaps the least understood advantage of all.
Chakra potency.
That was different from chakra reserves.
Fugaku found the easiest way to picture the distinction was as a well.
Reserves were how much water the well contained.
Potency was how much water you could draw with each scoop.
Two shinobi might possess similar total reserves, but if one person's chakra was denser, stronger, and easier to shape into high-output techniques, then those reserves were not remotely equal in practice.
The Uchiha were built around that advantage.
It was one reason advanced ninjutsu came so naturally to their elite alongside their high learning speed.
A-rank techniques were difficult for most shinobi not only because of control or complexity, but because producing the required output cleanly and repeatedly demanded chakra of sufficient quality.
The Uchiha usually had that.
Their Fire Release was the most obvious example.
Madara's future Majestic Flame Destroyer came to mind almost immediately.
An entire battlefield swallowed by a single fire technique.
That was not simply "having a lot of chakra."
It was what happened when reserves, control, transformation skill, and overwhelming potency were combined in one person.
That was also part of why the Uchiha had been able to contend with the Senju for generations.
Their combat philosophy almost emerged naturally from their biology.
Kill the opponent before endurance became the deciding factor.
Overwhelm them with visual perception.
Break them with genjutsu.
Read their movements.
Copy techniques.
Then finish the fight with high-level ninjutsu before a more physically gifted opponent could drag things out.
If that failed, then the Senju advantage became increasingly unpleasant.
Outlast the Uchiha.
Recover faster.
Keep fighting after the first exchange should have ended things.
That did not mean Uchiha chakra reserves were poor.
Far from it.
They only looked modest when compared against those descended from the "Sage's Body" inheritance clans like the Senju.
Against most of the shinobi world, the Uchiha still possessed excellent reserves.
The reason was obvious once Fugaku stopped treating "chakra reserves" as if they were a single independent trait.
Chakra was produced from both energy types.
The Uchiha's spiritual side was exceptional.
A useful way to imagine it was that physical energy provided the base while spiritual energy flowed through and enriched that base.
The stronger the spiritual component, the denser, "richer," and more effective the resulting chakra became.
Which meant greater spiritual energy did not merely improve genjutsu or dōjutsu.
It effectively increased how far the same nominal amount of chakra could go.
Less expenditure.
More result.
In practical terms, that made the Uchiha's usable reserves much larger than a simple comparison of raw stamina might suggest.
And the Sage Body clans had other corresponding advantages as well.
Beyond superior vitality and various physical benchmark leads, they also tended to possess a naturally stronger affinity for Yang Release.
In most shinobi, Yang Release appeared most clearly through medical ninjutsu.
They also had exceptional longevity, especially among the Uzumaki.
Fugaku now suspected there was another advantage too.
More 'flexible' chakra coils.
That idea came partly from what he had learned in this life and partly from old theories he remembered from Earth.
It would explain the Senju remarkably well.
Their famous ability to learn enormous numbers of techniques, elemental or otherwise, might not have come out of the blue.
Their chakra networks were, most likely, simply more 'adaptable' by nature, making it easier for them to pick up new ninjutsu and different chakra applications than most shinobi.
...
Anyway, Fugaku was not about to become "Yang dominant" merely because he intended to train his body far harder than ever from now each day.
If anything, the opposite side had already just received an 'instant', enormous boost as well.
Those three days had done far more than integrate memories.
They had strengthened his soul.
It felt almost like another hidden reserve of spiritual power had always existed somewhere deeper inside him, compartmentalized away in secret, holding the memories of his previous life, and the awakening had finally fused it with what Fugaku already possessed.
That was probably part of why he had remained unconscious for so long.
Physically, there was little wrong with him anymore.
His body had recovered quickly after that situation.
The real work had been happening somewhere deeper.
In the mindscape.
That strange internal space that acted almost like a container of the actual soul, where tailed beasts, in their spirit forms, external spiritual fragments, or in his case, his past life spirit buried deeply, and other things that did not belong purely to the physical body could exist.
The brain itself seemed to sit at another intersection.
Body.
Soul.
Chakra pathways.
All meeting in one place.
Which probably explained why genjutsu could interfere with perception and consciousness so effectively through specific chakra injection there.
Anyway, whatever the exact mechanics, Fugaku was certain of one thing.
His entire Yin side had massively strengthened already.
Not merely raw spiritual energy.
Everything well-known to be connected to it and aforementioned.
Down to the smallest detail too.
Memory formation.
Recall.
Willpower.
Mental endurance.
The speed at which he processed and organized information.
Both physical and spiritual energy naturally increased with age.
Physical energy grew as the body matured.
Spiritual energy grew through experience.
Quantity mattered.
Years lived.
Things learned.
Memories accumulated.
Which made the sudden arrival of an entire previous lifetime especially significant.
If those memories had truly been sealed away somewhere inside his mindscape, then it made sense that some corresponding spiritual strength had been buried with them.
Or, better said, it was all the same thing.
Now all of it was available at once.
Quality mattered too.
Difficult experiences.
Trauma.
Loss.
Pressure.
Challenges that forced someone to adapt rather than collapse.
Those could create sudden spikes in spiritual growth.
And the reverse was also possible.
A person broken by experience could lose that sharpness instead.
Fugaku had seen enough examples of both in the future to believe it.
So yes, even if he had simply continued living as before, he would probably have grown considerably stronger with just age.
After all, he was not even halfway there in his natural shinobi prime.
But that was no longer enough.
If challenging experience strengthened the spirit particularly well, then Fugaku had no intention of living cautiously enough to remain comfortable.
...
"Not to mention, the greatest proof of my spiritual 'upgrade', and probably the biggest reason for my confidence, is already right there..."
Fugaku's grin widened.
His open eyes remained fixed on the traditional ceiling above him.
Then, for a single second, they changed.
A brief, ominous flash.
And just as quickly, Fugaku closed them again.
He had not been particularly surprised when, the moment he finally woke and opened his eyes again, instinct told him that he had it.
Not because of those old Earth theories claiming Fugaku had possessed the Mangekyō in canon.
Most of those had always been speculation.
What convinced him now was everything else.
His pedigree within the Uchiha.
And what had just happened to him over the last three days.
His bloodline was prominent even by Uchiha standards.
Historically, in recent times, only Madara's direct lineage had clearly stood above it, and even then, perhaps not by as much as later history made it seem.
Madara himself had simply been absurd.
A freak among freaks.
Indra's reincarnation.
That naturally made everyone around him look lesser by comparison, including Fugaku's grandfather, who had been his contemporary.
But after Madara abandoned the clan and village not long after Konoha's founding, his own line effectively ended with him.
His brothers were already dead, and no direct successor remained.
It was Fugaku's grandfather who eventually took over as patriarch.
That alone said enough about where their branch stood.
But lineage was only part of it.
Fugaku himself was the stronger argument.
He had eventually fathered two sons who both awakened the Mangekyō Sharingan.
That was ridiculous when he actually stopped and considered the odds.
After Madara and Izuna, Konoha would go roughly half a century without another known Mangekyō awakening.
Then Fugaku's single household produced two.
Mikoto obviously contributed.
Her lineage was also respectable, elder quality even, and she was already exceptionally talented for an Uchiha girl of her generation.
At eleven, she was probably the most promising female Uchiha in recent years.
But Fugaku then mentally compared both of them at that same age.
And shamelessly, he considered himself the larger contributor afterward.
He had been more talented.
His lineage was more prominent.
Sasuke being Indra's reincarnation did not invalidate that either.
Reincarnation clearly did not create everything from nothing.
If it did, then every previous Indra reincarnation across history should have become another Madara.
They had not.
The vessel mattered.
The underlying body.
Bloodline.
Inherited potential.
Madara had possessed an exceptional Uchiha lineage before Indra's chakra ever became relevant.
Sasuke had too.
And Itachi made the point even more obvious.
No Indra.
No reincarnation advantage.
Yet he awakened the Mangekyō extremely young.
That had come from somewhere.
So perhaps the old fan theories about Fugaku possessing the Mangekyō had not been entirely ridiculous after all.
Not proven.
But certainly plausible.
Maybe this time he had simply reached the same destination early.
Far earlier.
And through a completely different trigger.
That part mattered most.
Because when Fugaku reconstructed the original timeline, there were surprisingly few opportunities for his future self to awaken it.
The Uchiha had been heavily restricted from the First Shinobi World War.
He knew that directly from this life's memories.
And judging by what he remembered from the future, their participation in the Second War had likely been limited too.
Fugaku himself was never meaningfully associated with that conflict.
Which left the Third Shinobi World War.
The worst major war Konoha would face in generations.
By then, pressure would likely become too severe for the village to keep sidelining one of its strongest clans.
Fugaku would finally be sent into real large-scale war.
That was the obvious window.
Battlefield trauma.
Loss.
The kind of extreme emotional shock associated with Mangekyō awakening.
It would also fit the later reputation he remembered.
Wicked Eye Fugaku.
That name had to come from somewhere.
The irony almost made him laugh.
The supposedly debauched Police Chief, kept away from the village's greatest conflicts until necessity forced Konoha to use him, might only then have awakened the power everyone feared.
But Fugaku had no intention of waiting another decade and a half.
Fortunately, after what happened in that warehouse and the three days that followed, he no longer had to.
Yeah.
His innate potential mattered.
But the warehouse incident was probably the bigger reason the Mangekyō awakened now.
The timing lined up too neatly with everything else.
The buried memories resurfacing.
His spiritual state changing.
The three-day internal transformation.
Fugaku suspected the Mangekyō had not appeared the instant he was struck, but somewhere near the end of that process, once everything inside him finally finished reorganizing.
Looking back, the trigger itself was almost excessive.
Spiritual trauma.
Something had entered him.
He could tell that much now.
Not ordinary genjutsu.
Not simple chakra interference either.
It felt closer to some fragment of foreign spiritual power forcing its way into his consciousness.
Physical trauma followed immediately after.
The punch.
The fall.
The impact to the back of his head.
Then the emotional side.
Confusion.
Loss of control.
Humiliation.
The shock of being taken apart so easily in front of his own subordinates.
His first truly ugly defeat.
Everything had happened at once.
Soul.
Body.
Mind.
Emotion.
And somewhere inside that collision, the barrier around the dormant memories had broken.
They flooded back.
His spiritual power surged with them.
And the Sharingan, already carrying the potential for more, jumped from two tomoe straight into the Mangekyō during the process.
In hindsight, Fugaku almost found it neat.
A complete accident.
A miserable one.
But probably the perfect accident.