The language of Japanese today has five vowels. They are short vowels corresponding to the english words, cat, bet, hit, got, hut. By coincidence, these vowels are similar in quality to the short Hakka vowels of the Sa Tdiu Gok dialect which covers most of the pronunciation found in Hong Kong and its environs as a whole.

In Japanese dictionaries, you are able to find that the sounds that hey borrowed from the chinese over the centuries are still preserved through their use in different aspects of society. The three major classification of borrowings are termed Go-On, Kan-On and Tou-On.

On Borrowing	Comments
Go	Go On travelled to Japan via southern Korea around the Southern Dynasties era of Chinese history, around the 5th and 6th centuries, and pronunciations have been fossilised by Buddhist texts. Two famous Japanese texts which were written before the coming of the kana symbols, that used the Go-On sounds are; the Manyoushu (Thousand Leaf Collection) and Kojiki (Ancient Chronicles 712AD)
Kan	Kan readings are the most numerous or 'productive'. My dictionary says that it comes from the 'Sui and Tang' dynasties, and pricipally from the capital at Chang An, and purports to be a 'northern' pronunciation. The corresponding time frame in Japan is about the Nara until the early Heian (710-900) periods of Japanese culture.
Tou	Tou On readings are from the late till post Tang period until the start of the Qing Empire, encompassing the Five Dynasties period, Song, Yuan and Ming dynasties. In fact Tou On may be called Sou On by some. (Sou here is the Song Dynasty.) These are mainly used for scientific and engineering uses.

In Cantonese like Hakka, the endings of the ancient sounds are also preserved. There are six consonant type endings that occur in both of these Chinese dialects, but in Mandarin - the 'standard' Chinese dialect of China and Han speakers today, four of these have been lost (see examples below).

The Japanese borrowings are testement to this since their borrowings stem from the 4th century onwards until recent times.

From what I gather through reading and learning the Japanese language in a piecemeal fashion, I have found the following:

Comment	final/initial	Character	Hakka	Japanese	English	Mandarin	Cantonese
Hakka -t ending = -chi or -tsu endings in Japanese.	-t		yit	ichi	one	yi	yat
			fut	butsu	Buddha	fu	fat
Hakka ~k ending = ~ki or ~ku endings in Japanese.	-k		yuk, zuk	iku	educate	yu	yuk
			lak	reki	calendar	li	lik
Hakka ~p ending = ~t~ or ~tsu endings in Japanese.	-p		hap	gat-, kat-	combine	he, ge	hap
			lip	ritsu	establish	li	lap
Most Hakka nasal ng~ initials = nasal g~ initial in Japanese.	ng-		nget	getsu	moon	yue	yuet
			ngi	gi	righteousness	yi	yi

Of the three endings, only -p seems to have been changed in Japanese. But there are relatively few words which have -p endings, compared with -t and -k endings. The ~t~ represents the small tsu kana which repeats the following initial of the following Japanese sound and so is not the letter t itself. E.g jikkai = ten times.