Board Thread:Questions and Answers/@comment-24919788-20140509022515/@comment-8986886-20140512233614

PrinceVertigo wrote: Unohana's zanpakuto does have a theme; acids and salves. She mentions that her Shikai is full of special restorative chemicals and acids that restore the body to full health when swallowed. Her Bankai is the same chemical Turned to Eleven. Instead of healing, the bloody goop is now acidic, and melts away at the body.

I suppose you're referring to ch.526 p.8, where Zaraki's flesh seemingly melts away to show his bones? Wasn't that just a reaction to him being exposed to Unohana's Bankai? She forced Zaraki to use his full strength, to be able to handle the power of her Bankai, and so the melting of flesh is merely symbolic to his self-imposed limiters fading away and exposing his true strength.

Besides, Unohana was also shown as a skeleton on that page, and I don't see why her own Bankai would harm her in that way.