Kashima Shinden Jiki Shinkage-ryu Heiho (鹿島神傳直心影流 兵 法) is one of the most powerful forms of Japanese swordsmanship. It places emphasis on posture, breathing, focusing the mind and spirit (kiai), and developing a powerful cutting ability. It has a very austere character, with kata that are very strenuous to perform and develop a hard form of internal power.
This site contains information about the practice of Kashima-shinden Jiki Shinkage-ryu as maintained by students of Dr. David Hall, who studied under Namiki Yasushi (並木靖), 18th generation headmaster of the school. Information regarding training opportunities can be found at the link above.
Jiki Shinkage-ryu was founded by Matsumoto Bizen no Kami during the late 16th century and regards itself as the "true" Shinkage-ryu. Its fourth headmaster, Ogasawara Genshinsai Minamoto no Nagaharu (小笠原源信斎源長冶, 1574–1644), spent 20 years in Beijing in the early 17th century, practicing Chinese martial arts, including the large and heavy kwan dao. Its 14th headmaster, Sakakibara Kenkichi (榊原鍵吉, 1830–1894), was bodyguard to the Shogun and keeper of Edo castle. Jiki Shinkage-ryu contains a profound training regimen focused around the development of kiai (気合), which can be regarded as the active complement of aiki (合気). At the same time, Jiki Shinkage-ryu has far fewer techniques than other systems of kenjutsu. Up until the late 19th century, Jiki Shinkage-ryu was a sogo-bujutsu, and included in addition to tachi and kodachi the practice of bo, naginata, yari, and yawara (grappling) in its curriculum. A focus on shinai sparring by its 14th headmaster, led to eventual loss of those additional practices.