Kuroko Koumori has killed 715 people, yet she escapes death row by proving she remains sane. Instead of execution, she is given a second chance as a State-Appointed Executioner working for the Tokyo police, tasked with tracking down and killing other murderers. Her partner is Hinako Tozakura, a cheerful girl who drives Ferraris with no regard for traffic laws or even gravity, and who calls her "Kuu-chan." Kuroko, by contrast, is a lecherous lesbian with sharp instincts and a real gift for killing. They make a strange pair, but hunting vicious serial killers is hardly a job for normal people.