User blog comment:Xilinoc/Ch. 668 - BIGGER,FASTER,STRONGER/@comment-7426210-20160401024231

Someone in Reddit, answered that. It is a good analysis on the topic. https://www.reddit.com/r/bleach/comments/2te6bc/yachiru_is_nozarashi_and_kenpachi_might_go_bankai/

But honestly, I am surprised that Yachiru is or maybe a Zanpakuto spirit.