Japanese beer culture has exploded over the past twenty years. Before 1994, a Japanese brewery legally had to produce 528,000 gallons of the stuff every year to qualify for a license, a regulation nakedly meant to hand the advantage to long-established corporations. This situation still exists, to an extent, in Korea; hence the dominance there of the near-flavorless Hite, Cass, and OB.
But if we've entered the golden age of Japanese beer, we've missed the golden age of Japanese beer advertising. That came before the Second World War, a time when, if the advertising industry needed drawing, painting, or lettering, it was done by hand.
Asahi, Kirin, and Sapporo were not known for their richly flavorful product, but could command richly evocative imagery for the posters and postcards that promoted it.
A robust market now exists for these antique pieces of advertising and their suitable-for-framing reproductions. Spend enough time hunting for them, and you'll start to notice that different brands often used the same pictures: what you'd thought of as "the Asahi girl" might well turn up on a Sapporo poster, and so on.
Now if you'll excuse me, I seem to have developed a sudden thirst for an ice-cold beverage of some kind.