Board Thread:Questions and Answers/@comment-24919788-20140509022515/@comment-6007020-20140512222350

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.