Uraken-uchi translates as “reverse fist strike,” but we prefer to leave it as uraken. The translation doesn’t do it justice, and there’s no real analogue to compare it too; it is a unique technique. Uraken has a single, oddly-specific application -- to punch people directly in the face from a close distance. In the clinch, there is no way to punch an opponent directly in the face without raising your elbow, and this results in a weak punch. Uraken meets this need.
To throw an uraken, first clench your hand into a proper fist. Rather than punching outward, towards the opponent, punch directly upward along your centerline up to neck-level, with your palm facing towards you. Then snap your wrist down and towards your opponent. Like all other techniques, uraken should be optimized for peak power by shifting between stances, snapping the hips, and employing synchronized breathing and reciprocal action.
[video of uraken uchi from the front and side]
When done properly, uraken will still look kind of strange. Don't worry -- this just adds the element of surprise.