The terms of "Setsuninto" and "Katsuninken" were originally used in the koan (a method to learn the secrets of Zen) of Zen sects such as "Mumonkan" and "Hekiganroku".
「殺人刀」（せつにんとう）と「活人剣」（かつにんけん）とは、元来は禅の『無門関』・『碧巖録』などの公案での用語である。