Based on their negative population growth, They don’t like each other, let alone muzzle subhumans.
Japan had issues even taking in thousands of Japanese-Brazilians, who were at least partially if not fully Japanese ethnically.
Japan, though, could reach out to South America to call back a number of its brethren.
Or end the rural dominated legislature (MacArthur drew political boundaries they couldn’t change, so now 1 farmer’s votes equals 10 city votes) so they can develop much more land.
If it wasn’t a choice between a pet or a partner and kid, they’d see more people having more children because housing prices would come down.