Board Thread:Questions and Answers/@comment-931054-20180417134051/@comment-2182964-20180716174754

It has been confirmed as much as it is ever likely to be. The novel -- Bleach: WE DO knot ALWAYS LOVE YOU -- states that Yachiru is, in fact, Kenpachi's Zanpakuto Spirit.

That said, there was a debate about whether or not this information should be treated as canon or not. Kubo himself provided details and concepts but the novel itself was written by Makoto Matsubara. Whether you choose to be regard them as canon or not -- I certainly do -- is entirely up to you as the reader.

For those wanting to research the matter themselves, there are indeed a number of unofficial translations to both Bleach: WE DO knot ALWAYS LOVE YOU and Bleach: Can't Fear Your Own World available via a quick google search.

Happy reading!