Kai is located in central Yamanashi Prefecture, orientated north-south along the banks of the Fuji River.

[2] Per Japanese census data,[3] the population of Kai more than tripled between 1960 and 2000 and has grown at a slower pace since.

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.

Kai has a mayor-council form of government with a directly elected mayor and a unicameral city legislature of 19 members.