Genetic Manipulation or Biomancy is a very risky, dangerous and at times unstable art that allows one to create a new entity from a previous one. Very few have mastered and many end up simply creating horrific babbling monstrosities instead of something that is actually stable.
For ECN13000, this is what he is known for, he is able to create anything that he is motivated enough to do, and at times people come to him for his great gift. Due to some rivalries, a mob boss had decided to get a upper hand and employed ECN13000 to create something, some form of biological weapon, offering his own daughter to be the subject of this transformation.
Knowing his full potential and capabilities, ECN13000 accepted and got to work. He delivered the final product within a heavy containment unit and warned of specific procedures that would be required to be taken to avoid collateral damage...knowing full well this person would not pay attention to his warnings, and not wanting his own work to be lost to the tides of consequences, ECN13000 followed them. And low and behold, he was right...the procedures were not taken care of and this new creature had slaughtered anything in her immediate area.
After some trouble, ECN13000 was able to get her to become a stable being...but her inner monster could still surface, the only thing needed to keep her from rampaging and mutating is simple...Don't create any form of negative reactions to her. Due to this, often Erza is kept in a drunken, happy or blissful state where she does not end up becoming a problem to her environment and herself.

Erza Valentine (C)  ECN13000
Original Design (C) AcidxCat