Re: Where did O-Sensei get his sword training?
As I note in HIPS, Sugino sensei recalls, post-war, accidentally meeting Ueshiba and the latter asking him to teach him TSKSR spear (which is, in fact, rather unique). Sugino replies that he is unworthy, he'll send his teacher, and Ueshiba replies that he'd rather learn from Sugino.
There are a couple of other ramifications that I discuss in the text, but here, it is significant to note that Ueshiba does NOT want to be formally initiated in the school, he does NOT want to learn the entire curriculum, he sees a certain something that intrigues him and he desires to incorporate this something in his own training regimen.
That, in a nut-shell, sums up how he learned various weaponry, post Takeda (which as much as anything was, it is fairly safe to infer, was Takeda's derivation from Hozoin-ryu sojutsu). And that, in itself is interesting - one of the first weapons he learned was jukendo, he learned spear from Takeda, and then, at the twilight of his career, he circles around with a desire to learn a very different version of spear.