Emiya Shirou... do you regret your naive foolishness?
Black Zetsu rarely communicated with people, but the person it communicated with most was Emiya Shirou. The thought of mocking him had been festering in its mind for a millennium. It had always considered Shirou its pawn, yet was betrayed and discarded on the eve of success. The feeling was unpleasant.
It had seen the crystal coffin collected by the Senju more than once. The last time was two years ago. It had snuck into Tobirama's secret chamber and, standing arrogantly before the coffin, mocked Shirou's naive foolishness.
Now, he was truly resurrected. It finally had the opportunity to mock him in person. And it was an opportunity to reactivate this pawn, the only one that could lead its plan to success.
However, at this moment, Black Zetsu dared not indulge in a moment of pleasure. It needed to carefully consider its choices. It had another new pawn: Madara Uchiha. This was a brand new pawn, proceeding step by step according to its plan. Though he had only taken the first step, it already had a mature plan on how to use him.
As for Emiya Shirou... he was a mature model. Back then, it hadn't needed to do anything, and Shirou himself had handled everything to destroy Ninshu.
Of course, it didn't know what state the resurrected Shirou was in. In this era, there was no body of the Sage of Six Paths for him to study, only the chakra reincarnates of Asura and Indra. But that wasn't a big problem. Shirou's true strength wasn't his power, but his genius mind, his human experimentation techniques derived from his research into medicine. Having witnessed the miracle Shirou had created with the Sage's body, Black Zetsu couldn't imagine a genius like him, with the theories it provided, wouldn't be able to solve the problem of the Rinnegan's birth.
The only trouble was... would Shirou still believe it after a thousand years? A monster that had lived for a millennium... its identity certainly wasn't simple.
Uh... he probably would. As long as it fabricated a good reason. For example, that it was the will of the God Tree. This rhetoric seemed not much different from Kaguya's will.
To be honest, does it even matter? Shirou knew of Kaguya's existence. Most people of that era did, revering her as the Rabbit Goddess who served the God Tree. When it deceived Shirou, it told him that chakra was not a power ordinary people could master and had to fall into the right hands. Who were the right people? Of course, the Rabbit Goddess Kaguya Otsutsuki.
Wait... did I even say that kind of thing? Black Zetsu tried hard to recall. It seemed it had really mentioned reviving the Rabbit Goddess to Shirou, because he had obtained power from the God Tree's remnants and also believed in it. I... I seem to have said too much back then!
The only secrets left were its true identity and the methods of how to revive Kaguya. Truly reviving Kaguya would require a sacrifice, a secret that could not be leaked. Fortunately, it had kept this secret. However, it was also because it had kept this secret that the plan had failed. But it had already leaked the idea of wanting to revive Kaguya.
Black Zetsu kind of wanted to sweat, a reaction a creature like it shouldn't have. It had been too young and naive a thousand years ago. So young, ignorant, and reckless... how could I have been so simple? To have been so straightforward with my pawn! It experienced the embarrassing feeling of an adult looking back on their youth.
At this time, did it even have a choice? No matter what Shirou was thinking, no matter how much confusion he had about its identity... it seemed it had to choose him. Because Shirou knew too many secrets, it could only choose him as its pawn. If he leaked the secrets, this pawn Madara probably couldn't be used either. Unless it hid forever.
Actually, Shirou would be fine. After all, this pawn was quite formidable. Back when it was dejectedly thinking the plan to revive Mom would never see the light of day, Shirou had appeared and illuminated its life.
"Wait... maybe it's just my imagination? Let's go check his crystal coffin first."
Black Zetsu's figure quietly submerged into the ground, heading towards Tobirama's secret chamber, a location it happened to know. Soon, it arrived. When it saw the shattered crystal all over the floor, the broken edges still new and untouched by dust, and the half-corpse vanished, it knew. Shirou had truly been resurrected, and it was definitely related to Tobirama.
That guy Tobirama... he really used half a corpse to resurrect Emiya Shirou. He wants to use him to treat the severely injured Senju Hashirama! Black Zetsu thought of the great battle, of Hashirama's injuries. It had already guessed Tobirama's purpose. That guy... he really found the right person! In the entire thousand-year history of the ninja world, if there was anyone who could save him... besides the Sage of Six Paths... it was probably only Emiya Shirou.
"Wait... something seems a bit off. Emiya Shirou is helping to save Senju Hashirama after being resurrected?" It recalled the conversation it had overheard. A thought suddenly popped into its mind that terrified even itself.
Senju Hashirama is the reincarnation of Asura's chakra. He quelled the wars, pacified the Warring States period, and re-created a world that appeared peaceful. This guy Emiya Shirou can definitely feel that Hashirama is the person who carries Asura's reincarnated chakra. He is willing to help treat him. Wait... this idiot Emiya Shirou... he can't possibly still believe Asura's foolish words at this point, can he?
This terrifying thought emerged, and Black Zetsu couldn't stay still. Its figure moved rapidly, burrowing through the ground. It was extremely anxious. If Shirou still believed that idiot Asura, how many secrets would he leak? It had to find him, to know his thoughts. If he hadn't had time to leak the secrets, it had to persuade him to return to their original plan.
As for getting rid of Shirou to keep the secrets... the thought flashed through its mind and was gone. How much power did the resurrected Shirou have? What if he recklessly leaked its secrets? Moreover, it really didn't want to. Compared to the troublesome new pawn Madara, the once almost successful pawn Shirou was just too useful. This was the easiest path.
After truly seeing Shirou resurrected, no matter how many thoughts arose in its mind, in the end, its thoughts were reduced to only one.
Persuade Emiya Shirou... to stand on its side.