Isn't Kenpachi's sword in constant shikai? I'm pretty sure that all Zanpatous look like normal swords until the Shikai's activated.
Kenpachi's has always had that unique look to it. I've heard that its in constant shikai, but since he can't talk to it, its power is limited and he can't control its state. Anyone have more input on this?
Kenpachi's zanpaktou is in
constant Shikai because he could not seal his tremendous amount of reiatsu. However, since he can't communicate with his zanpaktou he can't fight along side with it.
This does conflict with the idea that you must first learn your zanpaktou's name
in order for it to be released into Shikai which is why so many people are confused about Kenpachi's sword. However, Kenpachi said this himself so there is no reason to doubt what he said.
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Anyways, a bit off-topic,
I do have a theory for him reaching Shikai at least though:
Look at Kenpachi's history. He grew up without ever having a name. It wasn't because he didn't want one, it was because...he just didn't have one. Thus, he gave himself a name. It was the same for Yachiru. As a child she didn't have a name because...she just didn't have a name. Thus, Kenpachi gave her a name.
Personally, as far as I'm concerned, I don't think his
zanpaktou has a name considering that zanpaktous are manifestations of the Shinigami's soul. It's not a matter of it not wanting to tell Kenpachi what it is, but rather it has nothing to tell him.
During his days in Rukongai, because he had no name Kenpachi suffered from a lack of identity because he felt like he had no place in the world. I could draw the same parallel with his zanpaktou. It feels like it has no identity and thus it screams and cries out. A possible way for him to "learn his zanpaktou's name" would be to gift it with one just like he did for himself and Yachiru. It'd certainly follow the pattern.
As for Bankai, guys, it will never happen, get over it. That is a fact. Kenpachi,
even without knowing his zanpaktou's name and using
one hand, is already one of the stronger Captains. A Shikai is plausible (actually, to be honest even a Shikai is pushing it), but a Bankai is completely out of the question. If he achieved Bankai, then would become too strong. He'd be a loophole in the manga.