User blog comment:Xilinoc/Ch. 579 - THE UNDEAD 6/@comment-6916556-20140507185035/@comment-4207271-20140508060521

Just a couple things.

Yachiru's Shikai is entirely plausible, as an Asauchi can become anything, so a twin spirit Zanpakuto (That would make Sanpo Kenju the third confirmed one) that manifests the spirits is entirely plausible.

Kenpachi didn't seal his Zanpakuto, you can see the ax on his back in one of the final panels, wrapped like Zangetsu Shikai originally was.