[quote=Balance]
What did you see in those memories?
[/quote]

I meant like pictures, and diaries or stories. Apparently Crona had an abusive mother that performed science experiments on them and fused them with the black blood. The blood would take on a consciousness of its own, and their mother would lock Crona in a pitch black room until they were beaten and scared into insanity. That's why Crona doesn't quite look like they're in control while fighting. That zombie-like movement is because their blood is moving them instead.