Reference, "Ude Makikomi" (technique 4-3) of George Kirby, Black Belt Budoshin Jujitsu, Volume 4, Panther Productions, 1992.
Also, "Ude Osae Dori," page 95 of Dennis Palumbo, Secrets Of Hakkoryu Jujutsu: Shodan Tactics, Paladin Press, 1987.
Also, "Pistol Disarming," page 17 of Jorgensen, S.J., Police Jiu-Jitsu, Paladin Press, 1930 (reprinted 2005).
Step 1-3 of H. Godan is the inside block in back stance, the reverse punch, and the "flowing-water kamae."
The opening move of H. Godan may be interpreted as one of two common weapon-disarming techniques, both of which we should teach to our students.
Ude Osae Dori
Use osae dori is a Hakkoryu wristlock and armbar that closely resembles this application. This technique is also very similar to the ikkyo arm bar described in H. Nidan, step 7.
In step 1 of the kata, the enemy slashes at you with a knife held in his right hand. You stop the slash with an inside block, and then (step 2) stun him with a reverse punch acting as a metsubishi (blinding technique).
The punching hand (your right 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 3). Your right hand grips his knife hand, and your left hand grips his wrist. Your left elbow leans on his elbow, forcing a painful arm bar.
The pressure on his elbow makes him double over, under control. Use your hands to apply opposing pressure against his wrist. Your left hand shoves his arm to your right. Your right hand shoves his bent hand back toward the left. His hand, in serious pain, opens and releases the knife. With a little practice, you can scoop up the knife using your right hand at the instant of release. What you do with it then depends on the circumstances. A Shuri bodyguard would almost certainly "return" the knife to the owner, blade first. In a modern setting, such ruthlessness would get you into serious trouble.
Ude Makikomi
There is a second interpretation of step 1-3 that is equally as practical and fits the kata motions even better. Kirby calls it ude makikomi.
The enemy slashes with the knife as before. You block and stun, as before. Then slip your left arm down between his right arm and his body. Bring your left hand up behind his shoulder, and then settle strongly into the "flowing-water kamae." This locks his shoulder and forces him to double over, under control. Usually the knife hand ends up twisted behind his back. You can reach over with your right hand to dislodge the knife.
That's as far as the kata goes, but you might want to train your students in the other half of the technique. Turn to your right and apply downward pressure to his shoulder to take him face-down on the floor. You can then kneel with your left knee on his locked shoulder. His twisted arm lies in the fold of your left thigh, so that his knife-hand protrudes from the vicinity of your left hip. You can let go with your hands; the kneeling posture maintains the shoulder lock. Take the knife away at your leisure.