Let's review the dialogue between Lord Mads and BZ in chapter 678:
Examine the flow of the dialogue-
Mads: ...you were created from my will
BZ: my will is Kaguya's
Why didn't BZ say, "I am Kaguya's will"?
To me, BZ's line implies that BZ's will is Kaguya's will and not that Kaguya's will...