The solution to Japan's problem is mass import of highly educated, non radical people who are a net positive contribution to Japanese society. India, China, S Korea are good candidates.
At some point society will either reckon with its values and value raising children more highly, or generations of highly educated non radical people will keep wiping themselves from the gene pool until things balance themselves out.
This is an extremely bad idea.
It's hard to imagine two cultures less compatible. Indians would have a very rough time in Japan -- imagine being effectively ostracized and forever unable to integrate into society (and not only yourself, but also your descendants!) -- and the average Japanese won't last 10 minutes in India without having a nervous breakdown on account of unsanitary conditions, lack of personal space, interpersonal aggression, etc.
Color me skeptical.