RoseMary's Favorite

It was about these two girls... who were kinda like assassins. One of the girls was, i believe, a mob boss. It was a really gory manga, the girls would cut their victims in half, and guts would fly everywhere! I can't seem to find it though. I also remember that one of the girls had her bones replaced with steel? or some other material. Can't remember precisely, but she was an experiment, killed her creator, and was hella strong.

Thanks in advance.