On Blue Moon Island, Sasuke stood bare-chested as his Susanoo endured the pounding waters of the Takitsubo Great Waterfall. In its hands was the divine weapon that had pierced the Demonic Statue of the Outer Path with a single strike at the end of the Ninth Battle—the Earth Grudge Fear "compound bow," Heavenly Magatama: Compound Bow!
Sasuke said to Orochimaru, who watched from the bank, "Drawing this bow with the Wooden Human's strength involves too many steps. This time, I want to do it with Susanoo's own strength. What do you think?"
Orochimaru's answer was equally straightforward. "That would probably require a Perfect Susanoo!"
Sasuke held a hand over his left eye without touching it. "I figured as much. That won't be possible anytime soon..."
During the Ninth Battle, he had absorbed more of the White Cursed Seal's state four, successfully restoring his left eye from a Byakugan to a Sharingan... This was the configuration he would take into the Ten Battles!
And during the Ten Battles, he had to accomplish two things. First, he had to completely absorb the White Cursed Seal's state four and free his right eye as well.
Second, he had to wring every last drop from the Mangekyo whose sight had only lasted this long because of the yang seal! He had to push them to the brink of blindness, sealing their ocular power. Only then could he awaken the Eternal Mangekyō Sharingan by transplanting Fugaku's eyes!
So... no matter how he looked at it, Perfect Susanoo would have to wait until after the Ten Battles!
Whoosh!
The waterfall's powerful current washed over Susanoo's neck and back, split at its shoulders, and converged into a river around its waist...
Sasuke concentrated, considering how to find another approach through technique when he could not break through