I found your father listed as part of the 27th Battalion Replacements in the 5th Division Marines and Wounded in Action.
There is a chapter called "Arrival in Japan" in this book about the 5th Marines. They first arrived September 22, 1945 and skimming it, it looks like they first came to Sasebo. It had been heavily bombed and it was an undefended city of 200,000 when the Marines arrived, although there quite a bit of munitions factories, etc. underground that hadn't been hit.
Another chapter, "Spread of Our Occupation" shows arrows where Marines went in Kyushu (esp.) from Sasebo.Cities included Fukuoka, Beppu, Kurume, Saga, Omura, Karatsu, Moji, Senzaki, Yamaguchi, Oita, Saeki and the islands of Gotoretto and Tsushima.