Nero an orphan who has no interest in anything at all finds herself in a situation that she can't seem to escape. One day, a tall grim man named Eruno forced Nero to be his adopted daughter as he taught her to kill to create the best "representative" for his family. As the years goes by the girl who once lived a quiet life in an orphanage with her sister turned into a menace who doesn't know anything but killing and wreaking havoc to society.