It is unclear how much O’Sensei investigated the martial teachings associated with the family of his friend, Takaharu Kuki, head priest of the three mountain shrines of Kumano - and a well-regarded scholar of ko-shinto – but it is likely, at the least, that the esoteric, associated on-myo-do (in-yo-ho teachings) were a topic of conversation.
This familial Kukishin-ryu is descended from the primordial “eight Kyoto ryu“ [Kyo-Hachi-Ryu], centered around Kurama Mountain, just outside Kyoto – home to the legendary tengu, and to the king of the tengu: Sojobo. To these same primordial ryu, because of geography, most of the old traditions in the area around Tanabe, where O’Sensei grew up, would have belonged. As it turns out, it is common for ryu of this Kurama-dera tradition to have a concept of “aiki” – as Ellis Amdur has documented – and, actually, Itto-ryu, too, via Chujo-ryu, is of this lineage.
This means that, if O’Sensei at all investigated the esoteric, ki-flow traditions of Kukishin-ryu at the Kumano shrines, he was investigating – and he would have known this – the roots of the Itto-ryu body and movement so central to Takeda Sokaku’s art. And he would have been doing this, too, when he introduced kendo instruction to the Kobukan in the early thirties: old-style kendo being rooted in Itto-ryu – and particularly Hokushin-Itto-Ryu.
Now, traditionally – and Ellis Amdur, for instance, received such information inter alia from the current soke of the Kukishin-ryu - the Kurama-dera tradition is regarded as one of the three primordial, original ryu of Japanese martial arts – all three being composite ryu – in traditional Japanese thinking: a central kenjutsu surrounded by a whole constellation of adjunct arts.
And when O’Sensei on the one hand, studied Yagyu Shinkage Ryu (possibly, also, as an adjunct to Yagyu Shingan Ryu), and when he arranged, on the other hand, for two selected Kobukan students to study Kashima Shinto Ryu in the late thirties, he was actually studying the swordwork – and associated ki-flow - of the two other primordial traditions.
(And, indeed, for a while O’Sensei owned or rented a property at the foot of Mount Kurama – and made training trips up the mountain with students such as Tenryu and Shioda Shihan – and at this same time he already owned land in the uplands above and North-West of Kashima Shrine, and had an outdoor dojo there… we are talking about Iwama. And it was a local Omoto-kyo luminary – who had hosted the local Budo-Senyokai dojo – who helped him buy that land. And it was that luminary’s son who got to study Kashima Shinto-Ryu along with O’Sensei’s own son…)
All of which makes sense of the sometimes-repeated assertion that O’Sensei studied “all” the Japanese martial traditions.
And we can see all of this, too, as an attempt to go deeper than the art he had learned from Takeda Sokaku – by digging further into the past… but more widely, too…