Jitokuin-ryū (自得院流), also called Ninshin-ryū (忍心流), was the hereditary spear (槍術) art of the Yamaoka (山岡) house, a hatamoto/bakushin family of Edo. Its documented life is concentrated almost entirely in the bakumatsu generation, through three connected men, and it is known to the record through them rather than through any transmission history of its own.
Yamaoka Seizan (山岡静山, 1829–1855; given name Masami 正視, common name Kiichirō 紀一郎) is the figure who gave the school its reputation. He was reckoned an extraordinary spearman — the encyclopedic entries record a celebrated match against Nanri Kisuke (南里紀介), said to be peerless, that ran some four hours to a draw. He died young, at twenty-seven, in Ansei 2 (1855).
Takahashi Deishū (高橋泥舟, 1835–1903) was Seizan’s younger brother, born into the Yamaoka house and adopted into the Takahashi family, who trained under Seizan and carried the art into officialdom: sōjutsu kyōjukata at the Kōbusho from its 1856 founding, sōjutsu shihan-yaku from 1860 — the connection that brought this school into your previous question. He is one of the “three boats” of the late bakufu alongside Katsu Kaishū and the third figure here.
Yamaoka Tesshū (山岡鉄舟, 1836–1888), born Ono Tetsutarō, learned the Yamaoka spear under Seizan, and when Seizan died leaving only his sister Fusako (英子) in the house, Tesshū married her as adopted son-in-law and continued the Yamaoka name — which is why he carried the family’s Ninshin-ryū spear, though his lasting fame is as founder of the kenjutsu school Ittō Shōden Mutō-ryū (一刀正伝無刀流).
