The situation in the summer of 1945 is that some of the military leaders of the country were willing to make some kind of peace that preserved both kokutai - an obnoxiously open-ended commitment that could be anything from "keeping the imperial government totally intact" to "keeping the emperor even if only in name" - and national honor, whatever that meant.Situation in 1945 was completely different since Japan already lost large parts of the territories conquered in 1942 so they could not expect to hold on to these territories. Instead I think they proposed or discussed to propose to grant independance to all remaining SEA colonies and asked the allies to do the same ...
Problem with the 1945 negotiations was that the Japanese relied on the Soviets as mediators, which played for time to relocate their european troops to enter the war and occupy as much strategic territory in East Asia as possible before war between Japan and the allies ended ...
The Americans' problem was that they correctly understood that the Japanese government, IGHQ, and the Army and Navy hierarchies were far from of one mind on the topic, they believed that a coup attempt against any peacemakers was probable and would probably succeed, and they also wanted to demonstrate the immense power of the nuclear weaponry at their disposal, especially to the Soviets. To put it bluntly, even if the Japanese government had managed to commit to an unconditional surrender before the nuclear attacks on Hiroshima and Nagasaki, Truman and his advisors didn't believe in its willingness or ability to carry it through. As the abortive coup attempt shortly after the nuclear attacks showed, they were probably not wrong to think that way. Without the Soviet invasion of Manchuria and the American attacks on Japan, it's hard to conceive of the IJA and IJN uniting behind a peace policy acceptable to the Allied powers.