User blog comment:Xilinoc/Ch. 668 - BIGGER,FASTER,STRONGER/@comment-7606564-20160331172211

Well. I don't really know what to say. This is kinda bull that kubo is pulling this. I'd say it's pretty easy to interpret that yachiru is his bankai based off wording, situation, and various background elements. I'm not happy about it and I do believe it's bull, but let's try to see how this could have happened.

Young Zaraki fights unohana and caps his ability to make the fight more interesting. Now for the sake of conversation let's chase this theory that zaraki split off some of his power to create the being "Yachiru". If my memory serves, he met her not long after his battle with unohana. This right here demonstrates exceptional (albeit subconscious) control of his spirit energy. To actually manifest a seperate being, akin to lilynet and stark, takes skill.

Now as for yachiru having a shikai. I'll admit this theory is bull, but it's the most reasonable thing I can think of. What is there to stop a being, human, shinigami, artificial, or otherwise, from picking up an asauchi and using it for so long that the blade adapts and forms to this being's personality. Now if this is the case, I don't think Zaraki's bankai or shikai should gain any abilities that Yachiru had. That sword that yachiru wielded was her own sword that had molded to her. Now that she is dissolving as an entity, that sword is just going to be a master-less sword. Those abilities should not carry over to Nozarashi in my opinion.

Finally the disappearance and reappearance of Yachiru. I think it makes total sense for her to disappear before Zaraki first revealed his shikai. She was the physical container for his latent energy and he had to tap into that to use his shikai. So I'm gonna say yes, that was a logical disappearance and I'll forgive any plot-holes and sloppy writing.

Now for the reappearance. He has the shikai out, so I'm calling this conversation in the end as happening all in zaraki's head. Yachiru should not be back as a physical being, because that entity is no more. Her words that "he has not been using her properly" are actually very interesting. She existed as a physical manifestation of his spirit energy. Now correct me if I'm wrong but isn't that the exact definition of a bankai? To be a physical manifestation of the users spirit energy. Now typically the sword is the medium to which the shinigami funnels their power. So I'm assuming that yachiru is telling him to use the power stored in her, and direct it at his sword. He's already been manifesting his spirit (her) for as long as he's been a captain so I'm okay with him having bankai. He's essentially been going through the motions of having a bankai released for at least decades.

My grievances with my own theory. He did refer to his sword as a "he" in the arrancar arc. Maybe he was still too out of touch with his spirit to tell at the time? maybe it was bad writing? Maybe my theory is total bull? Who knows.