Kai is a city located in Yamanashi Prefecture, Japan. As of 31 December 2021, the city had an estimated population of 73,626, and a population density of 1,100 persons per km². The total area of the city is 71.95 square kilometres (27.78 sq mi).

Yamanashi Prefecture is a prefecture of Japan located in the Chūbu region of Honshu. Yamanashi Prefecture has a population of 817,192 and has a geographic area of 4,465 km2. Yamanashi Prefecture borders Saitama Prefecture to the northeast, Nagano Prefecture to the northwest, Shizuoka Prefecture to the southwest, Kanagawa Prefecture to the southeast, and Tokyo to the east.