Sagawa mentioned that he only saw two (2) training exercises by Takeda Sokaku, and even says he held back doing 'aiki' in front of him.
Now, later Sagawa made a point of telling Kimura (of Transparent Power) what Sokaku said about 'aiki.'
Was there ever a system to teach 'aiki'? What method did Takeda Sokaku learn by? Inquiring minds want to know.
What seems to be generally believed these days is that there was in fact a system for teaching aiki. But Takeda reserved teaching it to certain special students. Everyone else he just taught endless variations of mundane jujutsu technique. The special students included Ueshiba, Sagawa, and particularly Kodo, who was as vertically challenged as Takeda and a school teacher to boot. He taught these men the system for developing aiki when they spent time with him, studying in intense depth for relatively short periods of time. He admonished them not to give the secrets away lightly, particularly not to foreigners, because it was essentially very easy to pick up.
The secrets themselves came from either his father, or the man he was sent to live with, but as they were secrets no records exist of what they did or what it was before Takeda called it "Daito ryu."