Mark,
Back to kendo, you could also check the relationship between Ueshiba Morihei and
Nakakura Kiyoshi.
From what the late Kanai Sensei says in this
interview it seems Ueshiba looked into kendo/kenjutsu practitioneers as possible succesors. First Nakakura, later Mochizuki (who started kendo at the early age of five).