Although not taught to beginners atemi is the name of the punch used in Aikido. It is used to soften and distract the opponent by hitting nerve points. Every single aikido technique has many openings for atemi. But atemi is only used as needed. If your opponent goes along nicely then there is no need for atemi. Then again if you have a really nasty opponent, a well placed atemi will break his balance, soften him up and distract him enough so you can go along with your original technique. One of my favorite spots for hitting with atemi is under the arms at the upper part of the ribcage, where a nerve point is handily located. This will usually radically change the expression on the face of your partner from grim determination to pale, especially if he/she's a beginner.