The Shibuchari Ainu was an inordinately large and powerful tribe whose territory encompassed the Shizunai river basin in the southeast, and into parts of Monbetsu in the northwest of Ezo. Their chief, Sentaiin was described as an intimidating figure, wealthy, and politically powerful. He regularly fished and hunted in the neighbouring Hae territory. Something that was a point of great frustration to the Hae chief, Onibishi, who was unable to do much about it. After the death of Sentaiin his son, Kamokutain, took his place as chief.

Shakushain, who was born sometime in the 1580s, had been described in the Tsugaru unification record in Wajin vernacular as a ronin, or a warrior without a lord, but eventually served under Kamokutain as a village elder. A six year war broke out in 1648 after Shakushain killed one of Onibishi’s subordinates during a three day meeting between the two. During that time, Onibishi killed Kamokutain to exact revenge for Setaiin’s disregard for Hae territory. Shakushain assumed chiefdom over the Shubuchari Ainu after the death of Kamokutain. Shakushain continued to fight the Hae over the killing of Kamokutain until 1655 when a ceasefire was mediated by Matsumae Lord Takahiro at Fukuyama Castle. The Matsumae clan, who held a trading monopoly in Ezo felt obliged to intervene, lest the fighting between the two tribes disrupt their commercial interests.

For the Shibuchari, Wajin gold miners had been a particular point of contention, as gold mining operations on the Shibuchari (Shizunai) river were ecologically destructive, a resource that was particularly important. Shibuchari is derived from Shipe-ichan, meaning "a salmon spawning place" in Ainu. The Hae Ainu, living upstream of the river, were largely indifferent, and were in fact quite friendly to the Wajin miners. Onibishi counted the head of the gold mining camp, Bunshiro, among his friends.

The tentative peace between the Shibuchari and the Hae lasted until 1666, when Hae Ainu were caught hunting in Shibuchari territory, and tensions were escalated when Shakushain refused to provide a bear cub for the Hae’s iomante ritual. In 1667 a Hae Ainu with kinship ties to Onibishi was killed by Kanririka, Shakushain’s brother, for trapping a crane in Shibuchari territory. The family of the slain man demanded Onibishi avenge his murder, and rather than start another armed conflict, and on the advice of his friend Bunshiro, Onibishi instead demanded from Shakushain 300 tsugunai, atonement gifts. Shakushain snubbed him by giving him eleven.

In the background of all of this, and one of the reasons Ainu from different areas were so fiercely territorial and so willing to risk hunting in other areas was a resource vacuum that was created in the wake of the Matsumae being granted a trade monopoly over all of Ezo in 1644. Prior to this, Ainu had the option of trading hawks, fish, meat, and furs to whichever daimyo they pleased in order to get better deals. Once the Matsumae were granted a monopoly they immediately forbid Ainu canoes from Wajin ports, and set up trading posts in Ezo exponentially lowering prices they would pay for Ainu goods with a take-it-or-leave-it policy.

Along with an influx of Wajin gold minders, the Matsumae expanded their exploitation of the lands resources by netting the mouth of rivers to catch salmon before the could reach their spawning grounds. With lower prices and fewer resources, it didn’t take long to create a crisis for the Ainu, who began fighting among themselves.

That Onibishi was friendly with Bunshiro and the Wajin gold miners, who were openly hostile to the Shibuchari, in his area was of great concern to Shakushain, who suspected that the Matsumae viewed the rival Hae with more favour than they likely did, and was wary of an alliance between the two. Shakushain warned that he would crush Onibishi and the Matsumae if the Matsumae ordered him to be subordinate to Onibishi, as he knelt before nobody.

To defend against the perceived threat of a Hae-Matsumae alliance, Shakushain ordered the construction of casi fortresses along the Shibuchari river. With the Shibuchari-Hae situation escalating, the Matsumae felt compelled to intervene and were forced to pick a side. Bunshiro relayed orders from Lord Takahiro that Shakushain was to give Onibishi tsugunai. Instead, Shakushain took ten men up the river and killed Onibishi’s two younger brothers as they tended crops in the mountains. Onibishi fled to Bunshiro’s house, where Shakushain pursued him with a force of 50 armed men.

Bunshiro pleaded that Onibishi be allowed to give tsugunai, but Shakushain ordered his house burned down, smoking out Onibishi. Onibishi was cut down by arrows as he fled.

After the killing of Onibishi in 1668, two Hae elders, Chikunashi and Harou, hired an assassin to kill Shakushain, however the assassin never found the opportunity to do so. Instead, 30 Hae, along with Chikunashi and his mother, raided one of the Shibuchari casi, setting fire to the structure and killing Shibuchari as they fled.

In response to this attack, Shakushain sent Ehiteki, an elder from their Urakawa allies, to raid the Hae casi upstream of the Atsubetsu river. Ehiteki was forced to retreat after three of his men were killed by musket fire, leading them to believe that the Hae either had direct protection from, or were being armed by Wajin. The Urakawa returned with 120 men, instead lead by Tsunoushi, successfully taking the Atsubetsu casi.

With the Hae devastated, they appealed to Matsumae officials for weapons and other supplies, which the Matsumae refused. In 1669, Saru elder and brother-in-law of Onibishi, Utomasa appealed to the Matsumae again for aid, and again was denied, but they agreed to send intermediaries to attempt a de-escalation. However, Utomasa died of smallpox on his way back home, and the intermediaries were not successful, and reports came to the Matsumae that Shakushain had begun his rebellion against the daimyo, and to a larger extent, the Japanese empire.

Sources Walker, Brett L. The Conquest of Ainu Lands: Ecology and Culture in Japanese Expansion, 1590-1800. Berkeley: U of California, 2001. Print.