Kanagawa Prefecture Kaisei has a humid subtropical climate (Köppen Cfa) characterized by warm summers and cool winters with light to no snowfall.

After the Meiji Restoration, the area became part of Ashigarakami District in Kanagawa Prefecture and was divided into several villages with the establishment of the modern municipalities system on April 1, 1889.

Kaisei has a mayor-council form of government with a directly elected mayor and a unicameral town council of 12 members.

Kaisei, together with the other municipalities in Ashigarakami District and Minamiashigara city, collectively contributes one member to the Kanagawa Prefectural Assembly.

In terms of national politics, the town is part of Kanagawa 17th district of the lower house of the Diet of Japan.