"We know a lot," Orochimaru said calmly, "Perhaps you're not aware, but there lives an Otsutsuki on the moon named Toneri."
"Toneri?" Black Zetsu let out a sigh of relief, suddenly realizing these people probably hadn't learned everything about the Otsutsuki from Haruno Sakura, "Hmph, he's merely a descendant of Otsutsuki Hagoromo. Although he carries the Otsutsuki bloodline, he lacks the dual pupils and isn't worth fearing."
There exists a space-time corridor between the moon and the earth, something Black Zetsu was well aware of. He had quietly traveled to the moon after Otsutsuki Hagoromo's death.
Naturally, his goal was to ensure the extinction of Otsutsuki Hagoromo's descendants!
He had tampered with the will left behind by Otsutsuki Hagoromo!
They had sealed Mother; how could he let them off easily?
And Black Zetsu found his opportunity because Otsutsuki Hagoromo's descendants had actually split into a main family and a branch family—this gave him a chance.