Shotokan's Secret

Reference, "escalation of wrist-lock pain," based on extremely painful personal communication with Soke Justin Butler of San Ten Jujutsu.
Also, "Hiji Mochi Nikajo," page 105, Gozo Shioda, Total Aikido: The Master Course, Kodansha, 1996.

Step 4-6 of H. Godan are the inside block, reverse punch, and "flowing water kamae," all done to the right side. Step 7-8 is the reinforced block followed by the "X" downblock.

This is a follow-on lesson, building on the ude osae dori lesson of step 1-3:

In step 4 of the kata, the enemy slashes at you with a knife held in his left hand. You stop the slash with an inside block, and then (step 5) stun him with a reverse punch acting as a metsubishi (blinding technique).

The punching hand (your left hand) then reaches for the knife hand, and secures a jujutsu "pistol grip"
on the back of the hand. Your palm is against the back of his hand, and your fingers wrap around the little-finger edge into his palm. Now make the "flowing water" gesture (step 6). Your left hand grips his knife hand, and your right hand grips his wrist. Your right elbow leans on his elbow, forcing a painful arm ikkajo bar.

This time the opponent resists the arm bar by bending his elbow and pulling against your grip. In step 7, hang on tightly to his knife hand with your left hand, but use your right forearm to press his forearm back toward his face. This creates the nikajo (number 2) wrist lock, in which his arm bends to the shape of the letter "Z". Use your left hand to rotate his hand up and back toward his face. At the same time, let your right elbow slide up on top of his forearm (as if you were reaching for his face) and apply pressure downward on his forearm with your elbow. This position is called hiji mochi nikajo, and is very close to the prescribed morote uke posture of the kata. Most opponents will instantly tap out at this point.

But if this doesn't produce submission, you can escalate again in step 8. Still maintaining your grip on his hand, use your right hand to get a power grip on his wrist. Shove his wrist down and to your left, while shoving his hand down and to your right, using the classic "X" block gesture. This is so damaging and so painful to his forearm and wrist that he'll throw himself face-down on the ground, screaming for mercy.

These techniques seem like a surprising application for a reinforced block and an "X" block, but they are extremely effective and they follow directly from the opponent's attempt to escape the initial ikkajo arm bar. That's a very common situation to encounter. Our students should be prepared for it.