My great great grandfather was a chap called Arasuke Sone ( 曾禰 荒助). Sone was a reasonably prominent Meiji-era politician in Japan.
On the death of my grandmother, we came across some references to Sone (diaries etc) in the family store house, which had been left largely sealed from around the time of his death.
There are minimal references to his life online (Wikipedia etc), but I am struggling for more in-depth biographical information. I've travelled to the Hagi Museum in Japan to learn more about the extended Samurai clan, but beyond some brief references (similar to Wikipedia), there was quite limited information about Sone specifically.
I'm not sure if this is the kind of question that Ask Historians deals with, but is there someone out there who can point me in the right direction?
I can't point you in the right direction about finding more detailed information about your great great grandfather, but I think you should look more into Japanese archives (government-related if possible). From what I know about that period in Japan, they were very orderly and kept nice records.
I can tell you a few things about your great great grandfather, the institution he worked for in his later years, and what kind of effect he and the powers he worked with had on Koreans and Korean history, but I don't think you'd like what you hear. My viewpoint is very Korean and it doesn't paint your ancestor in a good light. You can PM me if it's still okay with you.
(I'm currently studying Korean history for the college entrance exam, but I'm researching a little bit deeper on my own.)