Board Thread:General Discussion/@comment-11398218-20140521105018/@comment-5398287-20150607230632

Coolishy777 wrote: Just because he can her her speak, does not mean he knows that the voice really belongs to his zanpakuto. Shinigami often hear their zanpakuto spirit but never hear it say it's name (or just aren't told). Ahem.

From cnet128's translation of chapter 527:

Voice: (...Kenpachi. // ...Kenpachi of Zaraki.) Kenpachi: Who's there?!!! // Who is that calling me?!! // Show yourself!! Voice: (...Finally, you are able to hear... // ...my voice.)

First off, Kenpachi didn't recognize the voice of Nozarashi at all; if Yachiru were its spirit, they'd logically have the same voice. Secondly, Nozarashi itself states that Kenpachi has never heard its voice until now. This isn't a case of "Kenpachi didn't know it was talking to him", it's "Nozarashi couldn't reach him at all". As far as I can tell, that throws your theory of Yachiru being Nozarashi right out the window.