Charles Hill wrote:
I have a short video of Kunii Sensei of the Kashima Shinryu and was struck by how similar he and Morihei Ueshiba moved with the sword. Kisshomaru Ueshiba studied the ryu and apparently showed his father what he had learned. Perhaps this was an influence as well.
I'll note here that Kashima Shin Ryu and Kashima Shinto Ryu are two different schools. Kisshomaru trained with instructors from Kashima Shinto
Ryu, and much of Morihei's swordwork from Iwama after the war resembles Kashima Shinto Ryu (although he never trained directly, he only observed classes).
Kashima Shin Ryu has links to Aikido through Seigo Yamaguchi, whose swordwork was influenced by the school, and through Minoru Inaba, who teaches a limited portion of the curriculum along with Aikido. There are no (to my knowledge) direct links to Morihei Ueshiba's swordwork.