this is quite a hard problem for Japan to solve tbh. it's a beautiful country, however originally they're not immigrant friendly, you can't even get a citizenship back then.
Because of the working culture, many of the younger generations are reluctant to have family, apart from that the stagflation is getting worse and hardly solved.
I'm not really sure what to do as a leader of Japan as well tbh, hopefully they find out what to do before all is too late