Another five minutes later.
When Seimei once again activated the power of "Human Dominion" and employed the "Mystical Palm Technique" to stimulate his cells' evolution, a sudden surge of eager anticipation welled up from within him. In that instant, he realized it was a sign he was on the verge of completely breaking through his limitations.
Without any hesitation, he opened his eyes and, just as he had practiced countless times before, picked up a nearby glass bottle. He injected a small amount of Yang Release chakra into it, causing the Hashirama cells inside to absorb nearly all of the nutrient solution. Next, he took out a syringe and drew up the thin layer of liquid from the bottom of the bottle.
Staring at the pale green syringe in his hand, Seimei took a deep breath and plunged it into the upper part of his left arm. Gently pressing the plunger, he allowed the Hashirama cells to flow into his body. Energized by the life force within him, the cells seemed to spring to life, ravenously absorbing his chakra before beginning to multiply wildly.
Seimei glanced briefly at his left arm. Beneath his skin, he saw twisted, root-like strands emerging—writhing like earthworms and multiplying rapidly in a most unsettling manner. Only because his body was so robust could he, with his immense chakra, barely manage to suppress the wild proliferation of the Hashirama cells under such crude conditions. Left unchecked, they might have grown into something far more than mere "worms"—even sprouts might have taken root.
However, this was only a temporary measure. Without further intervention, the Hashirama cells would eventually spiral out of control. Sensing a growing unease, Seimei quickly refocused his energy. He reactivated "Human Dominion" and, once again using the "Mystical Palm Technique," condensed Yang Release chakra—this time concentrating it in his upper left arm, where the cells had gathered—instead of allowing it to disperse throughout his body.
As the concentrated Yang Release chakra arrived, the Hashirama cells in that area became even more active. Just as they seemed poised to burst out of his body in a completely unregulated proliferation, an unseen force suddenly acted upon them. There was no doubt that this force was the power of "Human Dominion."
At first, when he was still weak and his Mangekyō Sharingan less evolved, using "Human Dominion" allowed him to control only his organs. But now, with his Mangekyō Sharingan continually evolving—combined with his enhanced constitution, spirit, and increased chakra—he could barely manage to control clusters of cells. Under the binding influence of "Human Dominion," the Hashirama cells immediately quieted down.
Yet, being remnants left by the God of Shinobi, even if they had undergone two or even three rounds of alteration, the imprint—the genetic signature—that the Thousand-Handed Hashirama left was still overwhelmingly potent. Thus, all he could do was suppress them; fully assimilating them into his body would be far more challenging. Of course, it was unlikely that these cells would ever harm him—in the worst-case scenario, if they ran amok, he could always rely on "Human Dominion" to forcibly expel them. For now, safety was not an issue.
The next step was assimilation. Yes, assimilation. When others fuse with Hashirama cells, there are essentially three routes:
1. Weaken the Hashirama Cells:
First, one can weaken the cells and then, using various drugs, gradually acclimate the body to them until a state of fusion and symbiosis is achieved. A classic example is Yamato, who was modified by Orochimaru from a young age, continuously adapting to the Hashirama cells until he barely managed to fuse with them. The eventual outcome depends on the individual's innate aptitude and the vigor of the fused cells—the higher one's natural talent, the more active the cells become, yielding greater benefits, and vice versa.
2. Rely on External Force:
A classic example here is Danzo Shimura. He crafted his Sharingan arm by leveraging the spiritual energy of the Sharingan to counterbalance the bodily energy of the Hashirama cells. By exploiting that fragile equilibrium, he indirectly controlled the power of the Hashirama cells. However, this balance was extremely delicate; even a slight fluctuation could lead to a complete loss of control. Thus, even though Danzo mastered this power, he typically had no choice but to keep it sealed.
3. Forced Fusion via a Bridge:
The third method is the one used by Uchiha Obito—employing a specially crafted White Zetsu as a bridge, relying on a third party's (Uchiha Madara's) overwhelming power and his own unyielding resolve to forcibly fuse with the cells. Undoubtedly, this approach carries the greatest risk—if it succeeds, it's a win-win; if it fails, it almost invariably ends in death. Nonetheless, if successful, the rewards are the greatest—not only does it yield a stable state, but it also allows one to inherit a portion of the Thousand-Handed Hashirama's power.
However, none of these three approaches suited Seimei. Although they appear to be distinct paths, in reality, they all involve passively managing the Hashirama cells. Seimei, however, despised passivity. He chose assimilation on his own terms—forcing the Hashirama cells to adapt to him. This might mean sacrificing the chance to inherit the full power of the Thousand-Handed Hashirama, but it ensured that he remained in control. While most wouldn't care, Seimei was different. Whether one called him fastidious or arrogant, he simply hated having remnants of another's power inside him. After all, even his former Byakugan had been assimilated into his own strength. Moreover, what did Hashirama cells offer besides a Wood Release ability? As he had analyzed before, it wasn't Wood Release that was impressive—it was the might of the Thousand-Handed Hashirama himself. Besides, the powers he already possessed were by no means inferior to Wood Release. As the old saying goes, what suits you best is best. Even if he acquired Wood Release now, he could never manifest it at Hashirama's level. Given that, there was no point in agonizing over it.
With these thoughts fleeting through his mind, Seimei swiftly refocused. He harnessed the power of "Human Dominion" along with the Yang Release chakra condensed by the "Mystical Palm Technique" to guide the transformation of the Hashirama cells, enabling them to gradually adapt to his body. One minute later, the power of "Human Dominion" hit its limit, and he halted the process. Feeling the Hashirama cells in his left arm beginning to stir again, he didn't hesitate—in an instant, he unleashed his power to forcibly subdue them.
After a short rest, once his Sharingan had recovered, he reactivated "Human Dominion" and once again employed the "Mystical Palm Technique" to continue assimilating the Hashirama cells. And so, minute by minute, time slipped by until half an hour later.