While Yanbai was dining with Sasori outside.
Madara Uchiha lay quietly in the bedroom farther inside, his eyes closed, looking peaceful.
Silence surrounded him.
A moment later, something strange seeped into the air.
Though invisible, the intense killing intent would certainly have registered on Madara's skin had he been awake.
A strange black substance appeared in the inner room, illuminated by the Artificial Night Pearl.
One patch appeared, then another.
Thick, pitch-black liquid blossomed like flowers across the walls of the inner room.
It was the black of cold, viscous filth.
Black slime, and a robe patterned with red clouds against a black background.
This strange mass gradually filled the otherwise deserted room.
Black Zetsu...
The one who appeared in the inner room was Black Zetsu, who had not shown himself in a long time.
An abnormally large quantity of slime, in masses of varying sizes, gradually gathered inside the black robe with red clouds, finally coalescing into Black Zetsu's humanoid form.
"...Mother said Yanbai had trained you into someone mild-mannered. Why don't I believe that...?"
Despite his words, Black Zetsu did not dare approach Madara Uchiha.
Madara Uchiha lay quietly on the bed, seemingly unconscious, without the slightest response to anything he said.
"Say... since you're willing to live in Yanbai's memories, you must be willing, right? You should be more than happy to help him escape this world, shouldn't you?" Black Zetsu continued, almost murmuring.
Black Zetsu merely spoke, never once approaching Madara Uchiha's bed.
He waited a little longer.
Madara Uchiha still slept quietly over there, without the slightest reaction.
As though bored, Black Zetsu suddenly turned away.
However...
When Black Zetsu tried to pass through the wall as he had on his way in, his hand met solid material.
Yanbai had made these walls with Shikotsumyaku.