I asked Kono sensei what was it that O-sensei could do that you could do if you learned the secret of Aikido. But he told me how, not what.
So what could he do that was based on "the secret of Aikido"? The only possibility I have in mind appears in this interview:
O-Sensei: Yes. I met him when we were making the rounds after a celebration marking the 10th anniversary of the establishment of the government of Manchuria. There was a handsome looking man at the party and many people prodding him on with such comments as, “This Sensei has tremendous strength. How about testing yourself against him?” I asked someone at my side who this person was. It was explained to me that he was the famous Tenryu who had withdrawn from the Sumo Wrestler’s Association. I was then introduced to him. Finally, we ended up pitting our strength against each other. I sat down and said to Tenryu, “Please try to push me over. Push hard, there’s no need to hold back.” Since I knew the secret of aikido, I could not be moved an inch. Even Tenryu seemed surprised at this. As a result of that experience he became a student of aikido. He was a good man.
Is that a clue?