This is a liqueur rather than a base spirit. It is already sweetened, so treat the suggestions below as a starting point and go easier on anything else sweet.
Pour this first
Ginger ale, tall over ice.
Carbonation carries aroma up out of the glass, so a highball shows an aromatic bottle off rather than diluting the point of it.
One part shochu to three or four parts of the long mixer, over plenty of ice, then the accent on top. If it tastes thin, go two to three next time.
What it tastes like
Liqueur from Nakano BC in Wakayama. Importer's tasting notes: plum. The profile below is built from the tasting notes its importer publishes.
plum
Sweet
2/5
Body
3/5
Aroma
4/5
Fruit
2/5
Floral
not described
Grain
2/5
Earth
1/5
Umami
1/5
Read from the words above rather than measured. Where it says not described, none of the sources behind this page mention it, which is not the same as it not being there.
Base
Kishu ume from Wakayama with mikan, steeped in shochu
ABV
12%
What to mix with it
This bottle is made with plum, not merely reminiscent of it. A mixer meets the plum first and the grain second, so read these as answers to the plum rather than to the barley or the rice. Tap a family to narrow it down. Every suggestion carries its reasoning, so if the reasoning does not convince you, ignore the suggestion.
A longer wedge is a family we'd reach for sooner with this bottle, worked out from its flavours rather than tasted. It isn't a score, or a comparison with other bottles.
Hoppy Beverage Co. has made it in Tokyo since 1948; at 0.8 percent it is legally a soft drink, and it is hard to find outside Japan. Chill the bottle, the shochu and the mug and no ice is needed.
Carbonation carries aroma up out of the glass, so a highball shows an aromatic bottle off rather than diluting the point of it.
Eden Foods sells it as Ume Plum Vinegar in most US supermarkets, and it is one of the cheapest things on this list. A bar spoon, and unlike a crushed umeboshi it can go into a shaken drink.
Plum is in this bottle, not just on its nose, so this doubles it rather than introducing it.
The brine off the umeboshi barrel, so it is the same fruit in a form you can measure
Dewazakura's from Yamagata plums, or Machida Shuzo's on Amami kokuto shochu. It does umeshu's job and leaves the glass drier, which matters when the bottle is already sweet.
Plum is in this bottle, not just on its nose, so this doubles it rather than introducing it.
Tart red plum rather than ume, so it lands on the note without umeshu's cooked sugar
Harder to find outside Japan than most of this list. Worth ordering or a trip to a Japanese grocery, and where something easier works as well, that comes first.
Ways to serve it
With soda
On the rocks
The bases with no family of their own: sake lees, chestnut, corn. There are no style rules on this page, which is deliberate. What each bottle is described as tasting of is doing the whole job, so the suggestions come from that rather than from anything the category is supposed to want.
Cocktails other people made
We haven't found a cocktail written for this exact bottle. These were written for other bottles, so each one says which, and what changes if you pour this instead.