Board Thread:Theories and Speculation/@comment-45444155-20200804084623/@comment-4912646-20200806013149

Yeah, that sentence should probably be changed since it's not entirely clear whether Black Zetsu actually became the TSB or simply receded away from Obito's hand. To me, the art has always made it look like Zetsu is sort of "evaporating" as the orb appears rather than simply moving up his arm, but all we can really say for sure is that the orb appeared when Black Zetsu disappeared, and then later when Black Zetsu reappears on his arm, the orb is no longer present.

That said, since this is the "theories and speculation" board, there is an implied relationship between the TSB and "materialised will" like Black Zetsu, so it's not entirely out of left field for the orb and Zetsu to be made of the same thing. It's just too bad we'll likely never get any answers now, since the databook didn't help and the Boruto manga doesn't seem the least bit interested in any of the TSB/will/Yin–Yang-related stuff.