What was the overall Allied plan to invade the Japanese home islands in 1945 called?

The overall Allied plan to invade the Japanese home islands was called Operation Downfall.

Operation Downfall was divided into two major phases. Operation Olympic was scheduled to begin with an invasion of southern Kyushu in November 1945. Operation Coronet was planned for March 1946 and targeted the Kanto Plain on Honshu, near Tokyo.

The planned invasion never occurred because Japan accepted the Allied surrender terms in August 1945. The atomic bombings, the Soviet entry into the war against Japan, Japan's internal political crisis, and the Emperor's intervention all formed part of the final surrender context.

Operation Downfall is sometimes confused with Operation Overlord, the Allied invasion plan for Nazi-occupied Europe. Overlord began with the Normandy landings in June 1944, whereas Downfall was never carried out.