For the first time since the 1920s (apart from that particularly bad week in 1945), Japan's population has dropped by nearly one million over the past five years. That's kind of bad news for the monoculture.
It is an indication that as the nation gets older, and people have fewer babies at a later age, a demographic crisis is looming.
When they hit the stage in which 35% of the population is over the age of 65, things are going to get really interesting. Part of the problem is related to their rural exodus; the country has only nine major urban areas, and the young people are leaving the farms and paddies and heading to the cities. Since they don't need kids to help out with the chores, there's not a lot of impetus toward procreation, and the fact that they are, for the most part, living cheek-to-jowl, crammed into tiny apartments doesn't help set the tone for romance.
It also means that their workforce will be continuing to shrink. And unlike Democratics here in the USA who "think" that anybody and everybody should get a free pass to enter the country with no health screening and no job awaiting, the Japanese take a very different view; only grudgingly tolerating those outsiders who make it through their very restrictive immigration standards.
Over the long term, it appears that that aspect of their culture is going to have to change if they are to continue to thrive economically.