i think your talking about one of the last few movements in sochin kata. and if you are, then i would say its exactly like any other punch in karate, the hikita pulls and twists on the collor or sleve or anything really, and the other hand punches. or, it could be used as a sort of "peel" in which the lead hand grabs the throat/eyes/any weak spot and the hikite arm grabs and twists the fingers/thumb in the elbow joint/any other weak spot and shears the opponent on two planes in an attempt to open his defences to frther attack. or both your hands grab the wrists of the opponent and pull them appart for a clear shot at his vitals, carefull with this one though, because he could still use his lags and head but.
if its not that slow punching action like near the end of sochin kata, then i got nothing. lol.
yours in life
its not supposed to make sense