Nuki-uchi ("Sudden Strike") is, like Kaishaku (and, under some circumstances, oikaze)an execution technique.

The enemy is bowing before you and expects the strike.  Rise up on your knees and onto the balls of your feet during the draw and spread them during kirioroshi, lowering and stabliizing your center as you strike. The sword must not touch the floor. Remain on the balls of your feet during Eishin-ryuu chiburi and noutou, sitting back onto your heels as the tsuba seats into the koiguchi. Draw the knees together and assume seiza. This technique completes the Shoden waza.