It improved.

I know that sounds strange, but the Japanese economy had been shoveling treasure into the maw of War for years.

The end of the War, as signified here by the two nuclear bombs, meant that whatever monies were left could be invested in rebuilding the country, instead of literally being sunk by American ships and planes. In effect, there was no place for the Japanese economy to go but up.

Having hundreds of millions of US dollars poured into rebuilding Japan sure didn't hurt, either.