Thank you for the wonderful comments. This essay became part of Dueling with Osensei, my first book. The only thing I would add, now, is a paragraph on the idea that aikido is a manifestation of the sword.
People usually think of this as “aikido is kenjutsu without a sword in your hands.” No. What I mean is that you become like a sword. Think of a swordfighter doing a perfect irirmi in the method I described regarding Itto-ryu “One place we see this is in kenjutsu, and an exemplar of it is in Itto-ryu (remember the deep ties that Itto-ryu has with Daito-ryu). As the enemy cuts, so, too, do I cut. Not “along” the same path. ON THE SAME PATH. Two objects cannot occupy the same space, and I, with greater power/speed/timing/postural stability, etc, take that space.”
If the sword is made of inferior material, it will bend and break, and even though your technique is perfect, you will die. Similarly, perfect irimi requires a “forged” body. Osensei practiced – and taught – specific methods of breathing and exercise to “temper” the body like iron becomes steel.
In short, to create irimi requires a body like a sword – forged and strong, in a particular way. How, otherwise, could Shioda Gozo, perhaps 130 pounds dominate much bigger men as he did – and clearly he did this beyond people merely taking “good ukemi.”