The US refused.
After dropping the bomb on Hiroshima and killing hundreds of thousands of innocent people, then the United States did accept the offer, allowing Hirohito to retain power and politically protecting him for 43 years (until his death in 1989), because of his value as an anti-communist stronghold in the region.
Hirohito was not alone. The US also protected and recruited thousands of members of the notorious SS-style military group, Unit 731.
https://en.wikipedia.org/wiki/Unit_731
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