What was the planned Allied invasion of Japan called if Japan had continued fighting in 1945?

The planned Allied invasion of Japan was called Operation Downfall.

Operation Downfall was the overall plan for invading the Japanese home islands if Japan did not surrender. It had two major stages: Operation Olympic, the proposed invasion of Kyushu scheduled for November 1945, and Operation Coronet, the proposed invasion of Honshu near Tokyo scheduled for March 1946.

The plan was never carried out because Japan accepted the Allied surrender terms in August 1945. Allied planners expected extremely heavy casualties, drawing on the fierce fighting at Iwo Jima and Okinawa. Japan was also preparing millions of military personnel and civilians for a final defense of the home islands.

The atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, and Japan’s internal political crisis preceded the surrender announcement. Operation Downfall is sometimes confused with Operation Olympic or Operation Coronet, but those were component operations within the larger plan.