The formative culture of a country is its subculture. Mainstream culture is about the present; subculture creates the future.
In Japan, there have been three seminal subcultures since the end of World War II in 1945.
The first was the politically radical one of the immediate postwar period. That was essentially a continuation of the proletarian movement in literature and art of the 1920s and early '30s that was snuffed out through torture and force by the militaristic government of the day. This postwar subculture was bohemian and decadent, given its impetus by writers such as Osamu Dazai and Ango Sakaguchi. For all practical purposes, the latter's death in 1955 brought the curtain down on it.