"Metsu" means more than the other Katana Weapon Skills. The kanji for the WS in Japanese is 生者必滅, which means "All living things must eventually die". In short it could also mean "Return to nothing". Shouja Hitsu Metsu has also been translated by multiple Japanese players to mean "Eliminate all living entities". In the english version, it is shortened from "shou ja hitsu metsu" to simply "Blade: Metsu".
Blade: Metsu shares its name with Final Fantasy VII's Yuffie Kisaragi's second level three limit break, "Doom of the Living" or "生者必滅."Source