It angers people to hear it, but societies with high wages and particularly those where women can work have awful birth rates. Education correlates to lower birth rates. The ones with high birth rates are the ones where people barely scrape by, the ones where workers have no rights, the ones where people focus on getting by today and not plan for a poolside retirement 40 years down the road, the ones where menstruating women are considered filthy and isolated for a week from the men, the ones where having loads of kids makes important figures in your religion happy and there's nothing that matters in life beyond that. You need to change your country to have one (or many) of these conditions to induce high birth rates.
The birth rates in Japan are really no different from any other first world country. The west simply has a massive amount of immigrants to supplant the losses of the barely reproducing locals. Those immigrants might have 2 or 3 kids, and maybe their kids will have 2 kids. Then it reverts back to the mean of 1.2 kids basically everywhere.
There's lots of talk on reddit and other communities that if every country were like (XYZ country they consider paradise) and gave loads of vacation, paid high wages, gave everyone free college and housing, etc that the problem would disappear overnight. But you look at the birth rates of the locals in those countries, and it's always 1.2-1.4.
Mass immigration is a band aid. It makes governments and corporations hope, pray, and potentially strong-arm other countries into being underdeveloped and oppressive in a way that causes high birth rates, and makes the people who live there desperate to find better lives elsewhere. People aren't mass immigrating to first world countries because they decided on a whim that they want to work there, like rich westerners do when they decide they want to retire in SE Asia and be pampered the rest of their life. They move to first world countries because their home country is not a place that makes them happy to live in.