Black Zetsu's mood was easy to understand. If it and Hagoromo Otsutsuki didn't share the same mother, it would have been screaming obscenities at the Sage of Six Paths right now.
How could he not be completely, utterly, finally dead after more than a thousand years?
For Black Zetsu, the Sage's appearance wasn't just bad news; it was the-sky-is-falling, my-entire-life's-work-is-about-to-go-up-in-flames kind of news.
The Sage was the one who sealed Kaguya in the first place. Black Zetsu knew its mother, and it knew for a fact that the Sage wouldn't be lifting a finger to help revive her. He was probably guarding against her revival!
With the Sage in the picture, how in the world was it supposed to execute Project Tsuki no Me?
Black Zetsu wanted to panic and hide. It couldn't even figure out what had gone wrong. Where had Shirou even found the Sage? It had seen Shirou steal the Sage's body with its own eyes!
Suppressing the cold dread in its heart, Black Zetsu looked at the infuriatingly calm smile on Shirou's face and carefully asked for the truth. "Wei Yuan... isn't the Sage of Six Paths long dead?"
It quickly added, "Wei Yuan, you are the only one suitable to execute Project Tsuki no Me. No one in this world can replace you, not even if the Sage were truly alive."
If it were possible, how wonderful it would be if the Sage would get as far away as he can...
"Death doesn't mean the soul perishes," Shirou lied with practiced ease, casually adapting the story of what happened to Hashirama. "When Hashirama died, he died with a lingering attachment to Madara, so his soul couldn't find release and return to the Pure Land."
Black Zetsu's mood immediately tensed. That... actually made perfect sense.
The bond between Hashirama and Madara was the stuff of legends. It was entirely plausible that Hashirama's obsession with Madara would tether his soul.
"So... the Sage of Six Paths appeared?" Black Zetsu's mind was a confused mess. "Can the long-dead Sage still influence the living world?"
"It seems so," Shirou nodded, his expression becoming uncharacteristically grave. "When Hashirama was on the edge of life and death, he met the Sage. The Sage sent him back with a message for me. He said my presence in this era is a variable he didn't account for, and that he must send me back to the Pure Land... because a great crisis is coming to the ninja world, one that he must prepare for."
Black Zetsu felt a sharp, stabbing pain.
That unfilial son! Why can't he just stay quiet after dying!
What greater crisis? Besides my mother, what greater crisis could there possibly be?
Did the Sage sense its conspiracy? Did he sense its plan to use Shirou? If Shirou returned to the Pure Land, who could it rely on? Madara? The man looked arrogant and more than a little unreliable.
Moreover, after Shirou returned to the Pure Land, would the Sage tell him the truth about Kaguya? After hearing that, would Shirou still trust it?
A giant, terrifying question mark appeared in Black Zetsu's mind.
Will I lose Emiya Shirou as a pawn again?
No. It absolutely could not lose him. It still needed to find a way to bring him back to the living world, a second time, and win back his trust. Because it still needed to get information about the Sage from him—how he could influence the world, how much power he had left, whether he posed a threat to Kaguya's revival.
This was bad. This was very, very bad.
The only person who could provide that information was the man who was about to return to the Pure Land. It had to find a way to revive him again. If not for Tobirama's Impure World Reincarnation providing a blueprint, Black Zetsu would have been in despair.
A new plan began to form: get the other half of Shirou's body and use Edo Tensei to bring him back.
The Sage of Six Paths was truly detestable. It and Shirou had been companions who trusted each other, but after the Sage interfered, it now had to start all over again. It had finally convinced Shirou, finally taught him to lie, finally saw the hope of reviving Kaguya... and in the end, that unfilial son just beckoned and wanted to take Shirou away.
And it could only watch. It even had to persuade Shirou to go see the Sage. After all, only Shirou could bring back the intel it needed.
"That guy..." The anger surging in Black Zetsu's heart was immeasurable. "Hatred" was far too mild a word.
"What's wrong, Black Zetsu?" Shirou's face was a mask of innocent surprise, as if he had no idea about the existential crisis he had just triggered, no clue about the frantic mental gymnastics Black Zetsu was performing to salvage its millennia-long plan.
"I'm just a little uneasy," Black Zetsu said through gritted, non-existent teeth. "What if the Sage has regrets? Besides, there's a gap between the living world and the Pure Land. Even if he's willing to help, all plans must ultimately be executed in the living world."
"If something strange happens, only Madara can execute the project. You've seen how arrogant he's become even before awakening the Rinnegan. I'm worried he'll let the project get out of control."
This was, of course, pure slander. Madara's arrogance was innate.
"Then what should we do?" Shirou frowned thoughtfully, completely ignoring the fact that Madara's execution of the plan had worked out just fine in his past life. "Then the next time I see him, I'll tell him about your existence. If an accident really happens, you can guide him to execute the plan."
Black Zetsu was also thinking about this. It had never appeared before Madara, only helping him from the shadows. It had always hoped Shirou would be the public face, while it pulled the strings.
But if Shirou left... it would have to guide Madara itself. It had considered impersonating Madara's own will once he awakened the Rinnegan, but it couldn't do that now. Shirou knew its true identity.
If he let slip that they'd known each other in the ancient era, Madara would smell a scam a mile away. And it couldn't claim to be Kaguya's will, either.
"I can't tell Madara I am Kaguya's will," it explained. "His personality is too arrogant. He would never allow a god to be above him. He might even choose to destroy our project. Wei Yuan, the only one Madara can accept... is you."
It turned its gaze to Shirou. "Only under the cover of your identity will Madara be willing to accept my guidance. Only your existence will make him approve of our peace plan."
Yes. Only Emiya Shirou. He was the most trustworthy person in the entire ninja world. No one would doubt his compassionate heart. Even the Sage of Six Paths paled in comparison.
Even a man like Madara Uchiha didn't think Shirou was a bad person and had always hoped to be allied with him.