Wonderful reply with a lot to consider. And I certainly do not wish to quibble about what is - in my opinion - "more" plausible. Nonetheless, a couple points:
Kimura: "it is said that Shiro Saigo won against jujutsuka by the technique called Yama-Arashi [mountain storm]. Is this a tehcnique of Daito-ryu?"
Sagawa: "No. I don't think so. . . . It's said that Aiki was transmitted to Takeda Sensei by Hoshina/Saigo Sensei, although I believe that it was actually Takeda Sensei who created it.
When I look at the photograph of Tanomo Saigo . . . , I simipy cannot believe that he could have done Aiki. Even when sitting, those who have been trained and those who haven't seem different. he might have learned a littel bit of the form only, but I think it was something that Takeda Sensei created. . . .Nor have I ever heard that Tanomo Saigo was a master. (Transparent Power, pp 119-120)
#2 - Mr. Obata clearly states that he made his version up.
#3 - no porcupines in Japan.
Just saying. Any reference to porcupines are the same as references to "arai-guma" -washing bears, aka racoons, well after sustained contact with America. I know, you were just having fun, but for the record.
Truly, where I come down to is this: Occam's Razor:
1. There was a jujutsu art in Aizu, which was an otome-jutsu. It has roots in Itto-ryu, which has had an IT training component for hundreds of years, related clearly to doctrines passed originally from China.
2. It was practiced by Takeda Sokaku's grandfather, who was the bujutsu teacher of Takeda Sokaku's father, who taught him martial arts, AND as a teenager, Takeda was winning sumo tournaments against brawny adults, before he had other bujutsu training. (Unlike Saigo, who couldn't even hang with Kano for very long, Takeda was running the line in tournaments, fwiw).
3. (All this aside from the psychological aspect of things which I proposed in HIPS).
4. All I'm saying is that there is this wonderful avenue of research that no one has tapped. If it's a blind alley, then one is left with, I believe, three alternatives.
a. Tanomo, after all
b. Takeda Sokaku, with all his training in so many arts, found the principle buried (he, too, resurrecting HIPS).
c. Takeda pieced it together from various partial transmissions from each of the various ryu he learned and audited.
But surely, as there are scholars on the history of Aizu and the Nishinkan, it would be a meritorious bit of research to find the substance of Shinmyo-ryu jujutsu and it's subset Inegami Shinmyo-ryu.