I don’t know how many were stationed in Japan but most got out. All I know is a lot of war-weary vets of the European theater were ready or in the process of deploying to the Pacific and lucked out. My Dad spent almost a year back in the states before he got out. I missed being a military brat by two months.
I expect enlistees had to serve out their time while draftees duty ended with the actual war.
I think we had nearly a million troops in Japan at the start of the occupation.