As the cytotoxin was injected little by little into his bloodstream, it reached a delicate equilibrium with the overwhelming vitality of the First Hokage's cells. Slowly, almost imperceptibly, the rampant erosion subsided. The once-devouring force finally quieted, its expansion halting within Senmei Asahi's body.
But equilibrium was not victory.
The fusion between Hashirama cells and his own tissues wasn't fully suppressed by the cytotoxin—it merely slowed to a crawl. The two forces inside him continued to test one another, each probing for dominance.
The process was destined to be long and arduous.
For the next few years, Asahi knew he would need to periodically inject the cytotoxin, guiding his body step by step toward perfect symbiosis with the First Hokage's cells, until he reached the level of stability Yamato once achieved.
He slumped back in his chair, exhaling quietly. The tension in his muscles gradually melted away. Then, spreading from his chest—the site of fusion—a wave of warmth began to flow.
It wasn't the coarse heat of fever or the raw burn of pain. It was… life.
An indescribable, radiant vitality coursed through his veins, expanding outward until it filled his limbs and sank into the marrow of his bones. His entire being shuddered at the sensation.
It was a tremor that began not in the flesh, but in the very core of his existence.
From the depths of his cells, from the tiniest threads of his chakra, came the feeling that something within him was awakening—a long-dormant part of his lineage responding to a long-lost call.
Asahi could feel it. His body was changing—undergoing an evolution both natural and unnatural, miraculous and terrifying.
The First Hokage's cells were no longer merely grafted onto his own; they were becoming him.
Through this fusion, he was stepping beyond the limits of ordinary humanity, bridging a gap that linked him—no matter how faintly—to the origin of all chakra itself: the Ōtsutsuki clan.
Ōtsutsuki Kaguya, the progenitor of chakra, had been the first being to awaken this power within a mortal vessel. Her blood carried the mysterious force that allowed humans to connect with the divine energy of the world—the chakra of the God Tree itself.
The Senju clan, descendants of the Ōtsutsuki lineage through Kaguya's son, the Sage of Six Paths, bore fragments of that power in their blood.
That mysterious current was not only an inheritance of strength—it was the key to the origin of chakra, the first resonance between the human body and the world's natural energy.
According to Asahi's years of study and inference, the God Tree was the true source of all chakra. When Kaguya consumed its fruit, she merged her essence with that of the tree itself. Her descendants, therefore, inherited a biological compatibility with the God Tree's energy.
(TL Note: In case you guys forgot, this mc has no knowledge of Boruto)
And according to the Nine-Tails' own words during the Fourth Great Ninja War, the chakra of the Ten-Tails—the God Tree's monstrous form—was in fact natural energy, the same energy refined through Sage Mode.
The God Tree, the Ten-Tails, and Sage chakra were threads of the same tapestry.
Following this logic, the descendants of the Ōtsutsuki clan naturally possessed the potential to harmonize with Sage chakra. The perfect Sage Mode was not something borrowed from nature; it was a forgotten inheritance of their bloodline.
Thus, Asahi's speculation—that the descendants of the Sage of Six Paths could perfectly master Sage Mode—was not baseless idealism. It was a rediscovery of what already flowed in their veins.
Asura and Indra, the Sage's sons, had divided his inheritance—body and spirit. The Senju descended from Ashura, inheriting the resilience and vitality of the Sage's physical energy.
By fusing with Senju Hashirama's cells, the reincarnation of Ashura himself, Senmei Asahi had effectively reconnected a broken bloodline link. Through that fusion, he had drawn infinitesimally closer to the God Tree's power—a very very very distant relative, but kin nonetheless.
The benefits were immediate.
His chakra reserves increased, subtly but distinctly. More importantly, something new began to flow through his network: vitality. Pure, radiant, self-renewing life energy.
He couldn't yet regenerate wounds as Hashirama had once done, but his body thrummed with potential. Every heartbeat felt cleaner, stronger. His fatigue dissolved faster, his breath steadier, his senses sharper.
'This vitality… it's alive,' he thought, marveling. 'So this is what lies beyond the limits of an ordinary body.'
The First Hokage's cells had stabilized at last.
Feeling their rhythm synchronize with his own, Asahi rose from his chair and began tidying the lab. He sterilized the instruments, cleaned the syringes, and sealed the remaining vials with care. Once the floor was clear of glass and residue, he left Konoha Hospital under the fading glow of sunset.
The night air outside was crisp. He walked in silence until he reached Konoha's open training grounds.
Even with the fusion complete, his strength hadn't yet increased beyond the rise in chakra capacity. Still, Asahi trained relentlessly until late evening, pushing his body through every form and technique he knew until exhaustion forced him to stop.
This next period, he knew, was critical—the observation phase. If no adverse reaction appeared, he could move forward. The next destination was Ryūchi Cave, where he would finally cultivate Sage Mode.
Until then, he needed to perfect the dosage and frequency of his cytotoxin injections. He also began preparing a portable supply, to ensure that if the Hashirama cells went out of control during his travels, he could suppress them immediately.
Three months later.
Asahi submitted a formal request for leave to the Fourth Hokage, citing a mission of long-term medical observation and training.
Technically, leaving the village without authorization was forbidden. But Asahi's standing—both as Tsunade's disciple and as Konoha's foremost medical authority—made the approval effortless.
Namikaze Minato granted it without hesitation.
In the past, Jiraiya had spent years wandering the Land of Rain, teaching the Akatsuki's founding trio, and no one had questioned him. Asahi's contributions to the Third Great Ninja War were monumental. His position in the Hokage's lineage and his wartime merits granted him privileges few others enjoyed.
…
Ryūchi Cave—a name that existed in the same breath as Mount Myōboku and Shikkotsu Forest. A legendary place where serpents reigned, and the ancient art of Sage transformation reached its most dangerous form.
In recorded accounts, Orochimaru had once come here to pursue Sage Mode, but his frail vessel had failed to endure the White Snake Sage's energy. Years later, Yakushi Kabuto had succeeded where his master had not, merging with the White Snake's power to achieve the perfect Snake Sage transformation.
Using the perception channel created by Reverse Summoning, Asahi located the coordinates that resonated faintly with the summoning formula—deep within the heart of a forgotten forest.
'So this is it.' he thought, walking the last stretch on foot.
He analyzed as he went. If his deductions were correct, Ryūchi Cave's Sage chakra was fundamentally different from that of Mount Myōboku.
The case of Jūgo was proof enough.
Because Jūgo's clan had lived near Ryūchi Cave, their bodies constantly absorbed Sage energy from the environment. But their natural absorption lacked balance, resulting in uncontrollable rampages. Instead of turning to stone as in Myōboku's failure state, those who lost control here went berserk—their will erased under the flood of energy.
That meant Ryūchi's chakra was more primal—more feral.
'And Kabuto's transformation…' Asahi grimaced. The image of Kabuto's grotesque, serpentine form came to mind. 'No. I'll never allow that.'
He pressed a hand to his chest, feeling the steady thrum of Hashirama's cells.
If his hypothesis was correct, his enhanced vitality and Senju connection would naturally harmonize with Sage chakra. He wouldn't need to transform his body into a monster to wield it.
Finding Ryūchi Cave was not difficult, but reaching it was another matter. A massive barrier enveloped the area—a pale shimmer that rippled like liquid glass. Only those who had signed a summoning contract with the serpents could pass through.
Stepping toward the edge of the barrier, Asahi closed his eyes and focused his chakra.
*Zzzt…*
The mark on his palm—the summoning seal he had inscribed when signing the contract from Orochimaru's scroll—responded. The barrier rippled open before him.
Inside lay an expanse beyond expectation.
Ryūchi Cave was vast, a hollow world unto itself. Massive stone pillars, carved by ancient hands, rose toward a ceiling veiled in mist. Luminescent fungi cast pale light across the terrain. It felt both sacred and dangerous—an ecosystem alive with serpentine presence.
As he stepped deeper in, a hissing voice broke the silence.
"Human," said a white snake as thick as a man's thigh, its scales glimmering under the cave's eerie light. "The White Snake Sage has been waiting for you."
Asahi's lips curved slightly. "So the rumors were true. She can foresee the future."
"Follow me." the serpent hissed, bowing its head before slithering down a winding corridor.
After a long walk through tunnels lined with carved serpents, Asahi finally arrived before the throne chamber.
There, on a colossal stone dais, coiled the legendary being itself—the White Snake Sage.
Its body was immense and pure white, its scales fine as silk. A luminous pearl rested atop its head, another hung from a cord around its neck. Long orange hair cascaded down its shoulders, and in its mouth rested a smoking pipe.
Its golden, slit-pupil eyes regarded him with something between amusement and hunger.
Senmei Asahi stepped forward, bowed deeply, and spoke with composure.
"White Snake Sage," he said. "It's an honor to meet you."
*****
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I am working on the following projects:
✓ Killed For 100 Years in Hueco Mundo, Aizen Invited Me To Soul Society!
✓ Naruto: Senmei Asahi
✓ Naruto: Uchiha's Intelligence Dealer
✓ Naruto: The Fifth Hokage Is Naruto's Uncle
✓ Naruto: Who Made Him a Ninja?
✓ Bleach: In My Second Reincarnation, I Became The Ninth Kenpachi
✓ To Love-Ru: Spoiler Route [R-18]
✓ Naruto: The Accidental Incubus [R-18]
✓ The Academy's Saint Is Too Popular, But He's Not the Protagonist [R-18]