Izu Oshima

Oshima, more specifically Izu Ōshima, is a volcanic island located south of the Japanese capital city of Tokyo, and is part of the Izu Islands, all of which are under the jurisdiction of the Tokyo Metropolitan government.

In Vivid Red Operation, it is the landmass closest to Blue Island, which is located just north of Oshima, and is the home of most of the main characters in the series.