Regarding birthrates/immigration: Help without conditions is wrong, I now think. NGO's should not be allowed to 'help in Africa' (and Afghanistan, ...) without making sure that the birthrates drop significantly. Providing modern medicine without enforcing the 'recipients' to adapt the culture/custom will lead to a desaster in those countries (and if 'everybody' migrates - in Europe also (will happen after my lifetime probably)).
Being an island nation, Japan is in a good position to control their borders tightly compared with other countries like Germany.
It then becomes a question of having a well-designed immigration process that selects young, healthy, highly-educated folks who, most importantly, must speak the local language fluently. Canada has a pretty good system in place for this.