They say events in Japan often foretell the future of a highly developed and urbanized society, could be parallel to the old "Japanese people are not having much sex" news in the past, we're just catching up.
You just linked to an article that debunks the myth that Japanese are less sexually active than other people. TL;DR: the study that started it all, claiming that 40% of Japanese are virgins, was limited to people who have never married and this obviously skews the sample greatly.
https://www.theguardian.com/world/2022/sep/14/record-number-... (Record number of young people in Japan rejecting marriage, survey shows; Rise in people aged 18-34 who don’t intend to marry has consequences for Japan’s low birth rate and depopulation concerns)
Regarding economics, the economist Paul Krugman was the first to say it, in an essay in 1994, when he suggested that the slowdown in Japan might reveal what was going to happen to all other advanced nations. It was an idea he then developed over several years, in a series of essays, and then finally when his predictions came true, he came out with a book on the subject:
> last stop before the planet Mars: In Japan, the world’s most technologically sophisticated society, the future has already happened, says Peter Popham