甲斐国
The area of present day Kai was part of ancient Kai Province and have numerous Jomon period ruins. During the Sengoku period, warlord Takeda Shingen built embankments on the Kamanashi River for flood control and to open up new rice lands. During the Edo period, all of Kai Province was "tenryō" territory under direct control of the Tokugawa shogunate.