Mount Asama (浅間山) is an active volcano in the main island of Japan (Honshu) and sits on the border of the Gunma and Nagano prefectures. It is Honshu Island's most active volcano and overlooks the resort town of Karuizawa, 87 miles (140 km) NW of Tokyo. The Asama Volcano Observatory (established in 1933), run by the Earthquake Research Institute, University of Tokyo, resides on the eastern slope of the volcano.
Mount Asama is roughly 85 miles (137km) north of Hakone, where Tokyo-3 is situated. In Episode 10, the Angel Sandalphon is discovered inside Mount Asama after the Earthquake Research Institute (presumably the Asama Volcano Observatory) reported seismic activity.