
The US plan for invasion, "Operation Downfall" [1], called for what planners expected to be an invasion with a million casualties on the American side alone. It was scheduled for 1 November 1945. On the Japanese side, "The Glorious Death of One Hundred Million" was a slogan.
The US side of that story is presented in "Thank God for the Atomic Bomb", by Paul Fussell. (1981) Fussell is a well-known essayist. He was in the Army during WWII, and he was in a unit scheduled for the invasion of Japan if the atomic bomb didn't work.
Look up "Operation Olympic". The first phase, the invasion of Kyushu, was scheduled for November 1, 1945, less than three months after the atomic bombing. This wasn't just planned; the equipment and soldiers were already in Okinawa and Saipan, the staging areas, and that invasion was going to happen if the atomic bomb didn't force a surrender. The operation was at least 3x the size of D-day and over a 500km sea approach. A million dead were expected on the Allied side. Far more on the Japanese side, because the defense was mostly infantry without enough heavy weapons, armor, or ammo.
[1] https://en.wikipedia.org/wiki/May_15_Incident
[2] https://www.uio.no/studier/emner/hf/iakh/HIS1300MET/v12/unde...
The reality is that there was a peace faction in the Japanese government who did want to surrender but the ultranationalistic Japanese military was quite firmly in control and was very much _not_ interested in surrendering, even at the cost of millions of Japanese military and civilian casualties involved in continuing the war. (It's worth remembering that the Allied aerial firebombing campaigns had already devastated every other major city in Japan and caused far more civilian casualties than both atomic bombs did; both the Japanese and Allied militaries accepted this as part of the toll of war.) The aim (and preference of all factions) would have been a peace treaty that let Japan keep its ill-gotten gains in Asia. It took an unprecedented direct order from the Emperor to initiate the surrender, over the objections of the military. Even the high level overview provided by the Wikipedia article has excerpts like "[On August 9,] The cabinet meeting adjourned at 17:30 with no consensus. A second meeting lasting from 18:00 to 22:00 also ended with no consensus. ... The cabinet debated, but again no consensus emerged." and "As August 14 dawned, Suzuki, Kido, and the Emperor realized the day would end with either an acceptance of the American terms or a military coup." that directly contradict the idea that Japan was eager to surrender.
And beyond that, at the last minute, a coup attempt was made by fanatics willing to defy even the Emperor in an attempt to prevent the surrender proclamation from being broadcast (the Kyuujou incident).
Does any of this sound like a Japan that was eager to surrender? No, and that's why war historians generally deride this theory, quotes from Halsey, Eisenhower, etc. notwithstanding. Even just reading the Wikipedia article would make this clear: https://en.wikipedia.org/wiki/Surrender_of_Japan
[1] https://www.amazon.com/Japans-Longest-Pacific-Research-Socie...
The key thing to understand is that nobody was firmly in charge. The 6-member Supreme War Council, with representatives of the Army, Navy, and the civilian government was running the war. They had been operating by consensus, despite severe disagreements. The civilian government was much weaker than the military. (This stemmed from the February 26, 1936 attempted coup. Long story there.) The Japanese army and navy never got along. A strong faction in the Army wanted to continue the war to the bitter end. (They tried a coup against the Emperor on August 14, 1945, just before the surrender, captured the Imperial Palace, and almost succeeded.) War Minister Anami (the Army head on the Supreme War Council) said, after the Hiroshima bomb, "I am convinced that the Americans had only one bomb, after all." After the second bomb was dropped, Anami still wanted to fight on, but the Emperor decided otherwise. Anami committed ritual suicide.
It was a close thing. If Anami had supported the coup, or the coup had succeeded in capturing the NHK radio station or the Emperor himself, the war probably would have continued.
It's a very strange story of decision-making under extreme pressure. No one was in charge. The Navy was barely talking to the Army. The civilian government had been sidelined from control of military matters years before. The Emperor was supposed to be a figurehead. And, as pointed out above, there was an attempted coup to stop the surrender.
