Japan could probably use a few less people. What they don’t need is unrestricted immigration to “fix” the problem.
Way its going—they will become a part of the Chinese Han Empire in the future—as they were in the past.
Hence more burdens on young workers, less and less babies, and when those young workers reach their own old age --- nada. Bupkis. It'll all go to the Robots and, maybe, the Muslims (once they claw their way up through the Philippines.)
Anyone wonder why robots are being developed for, especially, geriatric care?
Its odd how every commentator I read elsewhere, from left to right, all throw out the cliche that Japan is in decline (or will decline further) because it does not accept immigration. The Japanese are a very homogenous people. They smartly understand - if they brought in Africans or Pakistanis, they would immediately create an underclass that would NEVER become Japanese, would be constant outsiders, and would be a source of constant friction with the majority Japanese. Even in its so-called "decline" Japan will remain a stable, peaceful nation with a high-standard of living, because it has a common culture which will keep it that way.