Board Thread:General Discussion/@comment-11398218-20140521105018/@comment-5780397-20150818103634

This thread here contains all the hints that may support the theory of Yachiru being Kenpachi's Zanpakutou spirit: https://www.reddit.com/r/bleach/comments/2te6bc/yachiru_is_nozarashi_and_kenpachi_might_go_bankai/

Also, Yachiru might have gained an actual body due to Zaraki stealing the Asauchi from the corpse of a Shinigami, who had most likely started to pour his Reiryoku into it. What if Zaraki's problems with his Zanpakutou originated here?

Furthermore, Yachiru is immune to Kenpachi's Reiatsu, which is only natural, if you assume she is a manifestation of his sword, but nearly impossible if we consider her just a normal girl.

Finally, Guenal Lee's involvement in the story was kind of shallow and useless, but if we assume that both him and Yachiru are created by Gremmy and Zaraki, who would later face off against each other, the matter takes on a whole different meaning.

I'dd add that when I started watching the anime and saw Zaraki and Yachiru's first meeting, I became convinced that she was his Zanpakutou's spirit, like, I think, the majority of you, only this hypothesis ends up being dismissed or completely forgotten due to the lack of an explanation in later chapters/episodes.