Just look at the global population count. It keeps growing. We don't lack human at all. You just need to better distribute them.
We're on track to hit 10 billion by the end of the century and probably flatline from there for another century.
It's only a crisis, because of the inherent bias toward 'pure' Japanese as something terribly important to preserve. Let the culture evolve, and there's no real danger at all, other than the one of their own making.