For anyone who has killed as many people as Kuroko Koumori, it is certain that they have lost their sanity. In fact, by demonstrating that she remains sane despite having killed 715 people, Kuroko avoids the death penalty. Now granted a second chance to stay in society as a State-Appointed Executioner, Kuroko and a girl named Hinako Tozakura are tasked with hunting down other killers. While Hinako is a rather carefree girl who drives Ferraris without worrying about traffic laws (or gravity, for that matter), Kuroko—who Hinako affectionately calls "Kuu-chan"—is more of a lascivious lesbian with razor-sharp instincts and a remarkable aptitude for murder. The two appear to be the most unlikely of duos. However, burdened with the gruesome duty of eliminating vicious serial killers from the country, it only makes sense that the executioners would be anything but normal!