The Chōsokabe of Tosa, the Yamauchi Succession, and the Embedding of Musō Jikiden Eishin-ryū

Prior to the Battle of Sekigahara in 1600, Tosa Province on Shikoku was ruled by the Chōsokabe clan. Chōsokabe Motochika had risen during the Sengoku period to unify much of Shikoku before submitting to Toyotomi Hideyoshi in 1585 after the latter’s invasion; Hideyoshi allowed the clan to retain Tosa while stripping them of other provinces. Motochika served in Hideyoshi’s campaigns in Kyūshū, against the Hōjō, and in Korea. Upon Motochika’s death in 1599, his fourth son, Chōsokabe Morichika, succeeded as head of the clan and lord of Tosa.

Morichika’s allegiance at Sekigahara reflected the turbulent loyalties of the post-Hideyoshi era. Accounts indicate that he initially intended to join Tokugawa Ieyasu’s Eastern Army, recognizing the power imbalance, but circumstances forced him toward Ishida Mitsunari’s Western (pro-Toyotomi) forces. His messenger was blocked at checkpoints controlled by Western elements, and he was compelled to align with the Western Army. He commanded roughly 6,600 men and participated in earlier operations such as the sieges of Fushimi and Anōtsu, yet at Sekigahara itself his contingent saw little or no combat. Positioned near Mōri forces, he was obstructed by Kikkawa Hiroie (who was secretly aligned with Ieyasu and refused to advance), leaving the Chōsokabe largely inactive as the Western Army collapsed. After the defeat, Morichika attempted to apologize to Ieyasu but was stripped of Tosa; he later joined the Toyotomi defense at Osaka in 1614–1615 and was executed after its fall.

Tokugawa Ieyasu rewarded Yamauchi Kazutoyo (Katsutoyo), previously lord of a smaller domain in Tōtōmi, with Tosa (assessed at roughly 200,000–202,600 koku). The Yamauchi were outsiders from Honshū. Their takeover was marked by armed resistance from former Chōsokabe retainers, many of whom were rural warriors of the ichiryō gusoku type (part-soldier, part-peasant). Kazutoyo arrived with limited forces and required Tokugawa assistance to pacify the province. Resistance was suppressed through violence: reports describe executions, the shipment of hundreds of heads to Tokugawa headquarters, and the crucifixion of dozens of dissidents (later colorful stories of a massacred sumo tournament appear to be exaggerated or fabricated). Senior Chōsokabe vassals were largely banished or became rōnin; most lower and rural retainers were allowed to remain but were reduced in status.

In 1613 the domain formalized the rank of gōshi (country or rural samurai) partly to absorb and control these former Chōsokabe men. Gōshi held intermediate status: they could wear two swords and, if able to afford a horse, participate in certain military rituals, yet they lacked the right of audience with the lord and were clearly subordinate to the jōshi (upper or castle-town samurai), who were primarily Yamauchi retainers and monopolized senior positions. The Yamauchi were long regarded by many locals as invaders or outsiders; resentment of the new regime and residual identification with the Chōsokabe persisted into the Bakumatsu period. Domain administration partly retained elements of the Chōsokabe “100 Article Code,” and land surveys from the earlier era continued to underpin assessments, yet social discrimination between the two strata of retainers remained a source of tension and later political friction.

This dual structure of Tosa society shaped the transmission and development of Musō Jikiden Eishin-ryū. The school traces its roots to Hayashizaki Jinsuke Shigenobu in the late sixteenth century and received major development under the seventh-generation headmaster Hasegawa Chikaranosuke Eishin (Hidenobu), who adapted techniques for the contemporary katana and emphasized forms from tatehiza (half-seated posture). The ninth headmaster, Hayashi Rokudayū Morimasa (1661–1732), a high-ranking Yamauchi vassal who served successive lords beginning with Yamauchi Toyomasa, introduced the tradition to Tosa while in domain service in Edo and upon his return. At the behest of the Yamauchi, he brought the art into the domain; he also incorporated a set of seiza (formal seated) techniques associated with Ōmori Rokurōzaemon (drawn from Shinkage-ryū influence and Ogasawara etiquette), practiced alongside the existing curriculum as Ōmori-ryū.

Under Yamauchi patronage the school took root as Tosa Eishin-ryū and became a prominent, effectively official iaijutsu tradition of the domain, taught to members of the ruling family (with minor adaptations such as exaggerated leg movements to accommodate long hakama). It was received especially vigorously among the gōshi. These rural warriors, descendants in many cases of the displaced Chōsokabe retainers, maintained a practical and robust form of the art through the Edo period. The social divide between jōshi and gōshi may have contributed to later internal differentiation; after the death of the eleventh headmaster Ōguro Motozaemon, the tradition split into the Tanimura-ha and Shimomura-ha lines, with some later commentary associating the branches loosely with differing social or regional emphases within Tosa.

In the late nineteenth and early twentieth centuries, the Tosa context continued to define the school’s modern form. Ōe Masaji (Masamichi, 1852–1927), born in Tosa and trained in both branches as well as other local styles, reorganized the extensive curriculum (reducing and systematizing roughly 160 techniques into the Seiza/Shoden, Tatehiza/Chūden, Okuiai, and paired sets still practiced), combined elements of the two ha, and formalized the name Musō Jikiden Eishin-ryū during the Taishō era. The earlier political and social rupture—Chōsokabe defeat, Yamauchi imposition, and the creation of a stratified retainer class—thus created conditions in which a sophisticated iaijutsu tradition could be imported under official patronage yet sustained in practical form by the very gōshi who embodied residual local identity and martial continuity. The result was a school deeply rooted in Tosa’s distinctive history, preserved through the domain’s dual structure, and ultimately standardized for wider transmission while retaining its regional character.

The photograph accompanying this essay is of Hosokawa Yoshimasa (細川義昌) performing Tosa-ha shoden iaijutsu (土佐派正伝居合術, also identified with 無雙神傳英信流) at the Imperial Shōbukai dōjō. Date: 18 August 1913 (published in Bushidō no Nihon, Vol. 5, No. 9).