Board Thread:Questions and Answers/@comment-5303512-20191025210913/@comment-10330822-20191026062817

Her appearing before others is not strange, because part of the mastery of the Zanpakuto to Bankai is the manifestation of the Zanpakuto Spirit in the outside world. Renji did the same thing in front of Ichigo when he said he was close to achieving Bankai. So all Bankai users, in theory, can manifest their Zanpakuto Spirit outside their Inner World.

Theoretically, when Kenpachi stole the Asauchi that would become his Zanpakuto, he at the same time began being talked to by Nozarashi, which was before he met Yachiru, as Nozarashi was already in its sealed state when Kenpachi found the child Yachiru. It's possible that Kenpachi's immense reiatsu allowed him to manifest his Zanpakuto Spirit long before he knew its name. And Nozarashi may have helped manifest Yachiru in an attempt to "contact" Kenpachi since Kenpachi couldn't hear it. The fact Yachiru tapped on Kenpachi's sword when she first appeared is also suspicious.

Also, Zanpakuto seem to "learn" with their Shinigami. As Zangetsu said it reached its Bankai at the same instance Ichigo did, meaning Zangetsu may not have even been aware of its Bankai before then. So odds are the Yachiru manifestation didn't known her name because Kenpachi didn't, and it was only when Kenpachi finally heard the name that Yachiru regained her identity as Nozarashi. The only problem with that is how can Nozarashi speak its name to Kenpachi, if it is ignorant to its identity and name as Yachiru. It actually make Yachiru out to be more of a piece of Nozarashi, rather than the spirit itself.

As for her Shikai, Zangetsu also displayed powers, like clones, that Ichigo never used, making me think maybe Yachiru's "Shikai" is just an ability of hers, because while we heard a name, we never saw the actual release of Sanpo Kenju nor did her actual "Zanpakuto" even change, it just "happened". It's possible her "Shikai" are just manifestations and Sanpo Kenju is just one of her nicknames.