The two common species in the region in winter are Black-throated and Pacific, both of which are easier to find on the Japan Sea side of Kansai where mixed flocks occur in some areas and these birds can linger well into spring. Perhaps surprisingly I've only seen one inland diver, a Pacific on Lake Biwa.
A Pacific in the harbour on Mishima, Yamaguchi in May.
Great Northern and White-billed are rare in Japan and are very unlikely to occur in Kansai whereas Red-throated, though commoner further north, is more reasonably to be expected down here.
A confiding Red-throated in a small harbour in Hokkaido January 2013.