Workers were subjected to heat and humidity with very little to eat and beatings if they slacked.
According to local records, 123 Koreans and 15 Chinese died on the island between 1925 and 1945.
Hashima is one of several industrial sites awaiting inclusion on UNESCO's list of World Heritage Sites. South Korea, however, has formally objected to the island's petition for recognition due to its association with wartime slave laborers.
Former Chinese laborers are still trying to gain compensation and an official apology from Mitsubishi for their enslavement at sites across the empire during World War II.
To Japan's neighbors, the island, in its ruined eeriness, is a symbol of a war wound that won't heal.
To most Japanese, it's a decaying remnant from a forgotten time.