That is a good piece of sleuthing. The reason this crest would not be included in a book of crests is that there were only three generations to the Yamashina line before SCAP abolished it (along with all collateral imperial lines) in 1947, so this crest was only in use for 89 years.
I see another cigarette case with this crest, although that one is fully marked with silver purity and the maker's name. Is the OP certain that this one has no marks at all?
There is little doubt that both cigarette cases were associated with the third and last of the line, Prince Yamashina Takehiko (1898-1987), the so-called "flying prince" who was a lieutenant in the Imperial Japanese Navy. He went completely mad with grief following the death of his pregnant wife and unborn child in the Great Kanto Earthquake of 1923, and retired from public life in 1932. Evidently he was in and out of mental hospitals and was never see again publicly. He never remarried and died without issue. Wikipedia has a brief article on him: https://en.wikipedia.org/wiki/Prince_Yamashina_Takehiko