Yamanashi, Japan
Yamanashi Prefecture (山梨県) is a region of Japan adjacent to Kamakura and Tokyo. It corresponds to the real-world Yamanashi Prefecture. Yamanashi is often known simply as Koshu (甲州), which is a historical name for the same area. It is also sometimes known as Kai (甲斐).
Modern-day Yamanashi Prefecture is not universally considered part of the Kanto region, but in Assault Lily it's typically included in Kanto[1].
Yamanashi was overrun by the Huge and largely abandoned during the conflict known as the Koshu Evacuation; some of the former population now lives in evacuation zones[2]. The Garden of Kaiseizan continues to operate within the occupied territory.