itcharo machito - Kyushu

I am trying to trace my Japanese Grandfathers ancestors, he was from Kyushu. Married my Irish Grandmother 1918, served in the British Merchant Navy World War 1 and 11, deceased 1957.I have a seamans identity card with name and date of birth, very old photos of his Japanese relatives with writing on the back, and know that he was from Kyushu, can anyone give me any help or guidance as to how I may find information on tracing
Thanks and regards
Josie Monroe, United Kingdom