鎧袖一触

From 鎧袖 (gaishū, “armoured gauntlet”) +‎ 一触 (isshoku, “single touch”). Attributed to Minamoto no Tametomo, according to the Nihon Gaishi by Rai San'yō:

至如平清盛輩、臣鎧袖一触、皆自倒耳

If the likes of Taira no Kiyomori's comrades were to even slightly brush against the sleeves of my armour, they would all drop dead on their own accord.

• IPA^(key):

鎧(がい)袖(しゅう)一(いっ)触(しょく) • (gaishū isshoku) 

1. to defeat an opponent in a single blow^[1][2][3]
   • 2011, Craig L. Symonds, The Battle of Midway (in English), Oxford University Press, →ISBN, page 179:

     Instead, Genda Minoru, the resident strategic genius, replied with a boast: "Gaishu Isshoku". Literally this means "One touch of the armored gauntlet"; idiomatically, it connotes an easy victory.

   • 2011, Jonathan Parshall, Anthony Tully, Shattered Sword: The Untold Story of the Battle of Midway (in English), Potomac Books, Inc., →ISBN, page 145:

     All eyes turned to Air Officer Genda, whose internal reaction might well have been, "If that happens, we're in terrible trouble." But what he uttered instead was a famous Japanese military phrase: "Gaishu Isshoku (One touch of the armored gauntlet!)," meaning roughly "We'll wipe them out!"