What was the overall Allied invasion plan for Japan, had Japan not surrendered in 1945, called?

The overall Allied invasion plan for Japan was called Operation Downfall.

Downfall was the proposed plan for invading the Japanese home islands if Japan continued fighting. It had two major stages: Operation Olympic, the planned invasion of southern Kyushu, and Operation Coronet, the planned assault on the Kantō Plain near Tokyo on Honshu.

Olympic was scheduled for November 1945, while Coronet was planned for March 1946. Allied planners expected the campaign to require enormous forces and anticipated severe casualties on both sides. Japan prepared its own defense plan, Ketsugō, which called for intense resistance against an invasion.

Japan's surrender made Downfall unnecessary. The atomic bombings, the Soviet declaration of war, the Soviet invasion of Manchuria, and political decisions by Japan's leadership all shaped the final surrender. Operation Downfall should not be confused with Operation Overlord, the Allied invasion of Normandy in 1944.