Perhaps you can enlighten what part of their culture makes them "fade away"?

Well the lack of focus on family and making it economically, culturally and politically beneficial to younger people especially women to have children would be an extremely obvious one.

What do you mean by lack of focus on family? Having lived here for the better part of a decade I've seen the opposite and tend to view it as one of the defining characteristics of Japanese culture.

Things are changing policy-wise to make it easier to raise a family. They're moving fast in that regard and I've witnessed many of these changes firsthand since becoming a father, especially where paternity leave and childcare payments are concerned.

Exactly my question as well. Rarely you can find a country on world map where family values are cherished more. Luckily Japan has none of feminism, pronouns and related stuff.