Question: Fuji Five Lakes (富士五湖 , Fuji-goko ) is the name of the area located at the base of Mount Fuji in the Yamanashi Prefecture of Japan, a point of interest is Aokigahara Jukai Forest, Aokigahara (青木ヶ原 ) , also known as the Suicide Forest or Sea of Tree, is a forest on the northwestern flank ,of Japan's Mount Fuji thriving on 30 square kilometers (12 square miles) of hardened lava laid down by the last major eruption of Mount Fuji in what year?
Answer: 864 CE