During one of my first stay in Japan, I asked my friends what kind of typical beverage I could try during the dinner to change from "nama beer" (witch is very good in Japan). My friends told me to try "umeshu"梅酒. It's a Japanese liqueur (not plum wine, because very sweet) made from steeping ume fruits (while still unripe and green) in alcohol (焼酎 shōchū) and sugar.
Then I tried and just loved it. When I came back to France, I was in Marseille, and cannot find umeshu there, but now I'm in Paris it's so easy and I always have a bottle ;)
And with Umeshu, I learn a very important word in Japanese (just kidding). One day, I was with Gentiane at the little supermaket in Nezu (where she first lived in Tokyo), we didn't know which one to choose, and try to explain to someone we would like the best one, then he said "ichiban" what it means the first one. So now when I'm in Japan and look for something I always ask for "itchiban".
In the restaurant, for umeshu on the Rocks just ask: umeshu rokku. Kampaï.