The Soviets entering the war was not enough to push the Japanese to end the war:

> These differences continued to be examined and hope of favorable word from Russia had been all but abandoned when very early in the morning of 9 August the news arrived that Russia had declared war. Although considerable pessimism had prevailed regarding the outcome of the negotiations, the Government was not prepared for war with the Soviets, nor the military capable of any effective counter-plan. Suzuki calculated that he had a choice of resigning or taking immediate positive action, which could be either declaring war on Russia and continuing until the whole Nation was destroyed or accepting the Potsdam Declaration.

* https://www.history.navy.mil/research/library/online-reading...

The Japanese were willing to declare war on the Soviets even though they knew they could not win.

Further, they new they could not win in 1944:

> Rear Adm. Soichi Takagi, who was attached to the ministerial secretariat of the Naval General Staff, made a study between 20 September 1943 and February 1944, of the war's battle lesson up to that time. He conclude that Japan could not win and verbally presented his findings in March 1944 to Admiral Mitsumasa Yonai and Vice Adm. Seibi Inouye. Takagi's study, interestingly enough, was undertaken at the end of the second year of the war--the time beyond which, the Japanese Navy's top command had estimated before hostilities, Japan could not fight a successful war. Takagi's estimate was based on an analysis of fleet, air, and merchant ship losses suffered to date, the serious difficulties in acquiring essential imported materials, the internal confusion in Japan, and a growing feeling among the "intelligentsia" that Tojo should be let out. It seemed clear to Takagi that potential long-range air attacks on the home islands and Japan's inability to import essential materials for production had created a situation which dictated that Japan should seek a compromise peace. In Takagi's view Japan at this time should have envisaged withdrawing from China and giving up both Korea and Formosa as part of the peace terms. His study in any case documented the fears Yonai and others held before the war and lent support to the increasing but still carefully guarded concern of their fellow Jushin that all was not well with Tojo's prosecution of the war.

* Ibid

Yet they continued to fight in the hopes of grinding down the US' / Allies' will to fight and get better terms.

There are no sets of facts that support the hypothesis that the Japanese would be willing to surrender without first being beaten down mercilessly. That beating could have been done in the 'traditional' way with troops, or with the atomic bomb. The estimates on the land invasion:

> The U.S. Sixth Army, which would invade and occupy Kyushu, estimated 124,935 U.S. battle casualties, including 25,000 dead, plus 269,000 non-battle casualties (disease, accident, etc.) for Kyushu alone. The JCS came up with an estimate that a 90-day campaign on Kyushu would cost 156-175,000 battle casualties, with 38,000 killed in action. By late July, the JCS was forecasting 500,000 casualties at the high end and 100,000 at the low end. In late July 1945, the War Department provided an estimate that the entire Downfall operations would cause between 1.7 to 4 million U.S. casualties, including 400-800,000 U.S. dead, and 5 to 10 million Japanese dead. (Given that the initial Downfall plan called for 1,792,700 troops to go ashore in Japan, this estimate is indeed most sobering, and suggests many more troops than planned would need to be fed into a meat grinder).

* https://www.history.navy.mil/about-us/leadership/director/di...

The US (Truman and others) concluded that they were not willing to have Allied troops suffer just the Japanese refused to accept the reality that they were beaten. And while the deaths of a few hundred thousand Japanese from the atomic bombs is regrettable, the lives of several more million Japanese were spared.