If Japan had had such a weapon it would have used without haste or regret. Dropping those bombs saved my late father-in-laws life. He was in the Fourth Marine Division and had survived being wounded on Iwo Jima.
Japan had the will to fight by means of brute manpower, but not this kind of technology.
And privately, a lot of Japanese were glad in retrospect that they weren’t pressed into a suicide effort. They probably had little idea of a “gracious conqueror.” The USA with Judeo-Christianity was familiar with the idea. Shinto did not support that.