This is commonly referred to as a "Ukemi" in other games. Basically you press X as you are launched in to the air to recover quickly. As the description states, you must do this 30 times in a single battle rather than across all plays. I'd wait until your level was much higher to do this, however I did it relatively early on during Mission 7 while grinding for souls. If you allow Kenpachi to launch you in to the air quite a bit and make good use of the health in the pots this won't be much of a problem. The higher your level, the less risky this is especially if you put your soul points in to defense bolstering nodes.