Board Thread:Questions and Answers/@comment-24919788-20140509022515/@comment-2120712-20140913000322

Healing can hurt. If the body's cell divide faster than the body can handle then you get cancer. Also it seems she can focus her shikai into a blade form seeing as she was killing him and healing him and not once did we see that creature, sort of a healing cut. Her bankai could take those healing abilities to the nth degree to the point that the healing becomes harmful think of it like the target suddenly growing grotesque growth or limbs on their bodies. Though we were shown the opposite with her usage, I think the blood we saw the bankai produce is infact all of the wounds she has healed over time so maybe her bankai ability is to fight using the blood of those it has healed in the past. Sort of like how Yama's Bankai remembers all those it has killed in the past and recalls them through its South ability.