User blog comment:Kurare/Yoruichi Shihōin's Zanpakutō theory/@comment-24113610-20140821173926/@comment-24113610-20140824214716

I still think your idea is grasping at straws. There's never been any hint whatsoever that she might be able to turn into something else other than a cat. Think about it. Byakuya called her a were-cat. If it was known she could turn into other animals, wouldn't he have called her something along the lines of a were-creature or even a shape-shifter?

And I guess calling her powerless in cat form isn't exactly accurate, but considering Yoruichi's never attacked someone in cat form, it's safe to assume it's only truly good for surveillance and reconnaissance, not battle.

Actually, now that I've read it over, your post actually doesn't make sense at all. We saw her transform back into her human form after Ichigo asked her how she bandaged him. And while we didn't actually see her transform, she changed back into a cat in the hot springs while Ichigo was training for bankai. She didn't say a release command and she didn't have her zanpakuto near her. She just changed.

So I stand by my point that her transformations have nothing to do with her zanpakuto. I have no idea what it her shikai could be but I'm inclined like most everyone else here to believe it has something to do with lightning.