I think the sum total of all of this (beyond my post, to be sure) is that kokyu-ryoku was O-sensei's personal interpretation and development of this "thing" called aiki.
You have said this before.
Kokyu is in Daito ryu
Kokyu is discussed in interviews with Daito ryu teachers
As you noted, here was Shioda -a prewar student- discussing Kokyu
1. There is no evidence that Ueshiba's kokyu was different than those who taught him and his peers under Takeda.
2. On what basis and teaching can it be demonstrated to be different?
3. You state here that Kokyu was O-sensei's personal interpretation and development of this "thing" called aiki.
Yet he personally stated that the source of aiki was:
Six directions expressed in a circle of opposing forces
Was heaven/ earth/ man and the mountain echo
That the mystery of aiki
is revealed with spiral energy rising from the right / descending on the left creating a friction in the body from which is born, in yo- (which in other passages he calls, aiki).
Now...he does in another singular
reference cojoin breath power in conjunction with spiraling.
I can make a case that kokyu is part of all of the above, but I would never make the case that breath power is
In sum, it would appear that Ueshiba's Kokyu was not
his discovery or creation- it was discussed and trained by his peers in Daito ryu-still the most probable place for him learning it. Nor does he himself consider kokyu his interpretation of aiki
and he never said it was. What he actually did say appears to contradict that. This is logical since aiki is in fact more complicated than breath power alone.
In a related topic to that; there are reasons that he looked and moved markedly different from Tohei, and the reasons are expressed in both of their writings.