Japan is changing very rapidly due to its demographic transition.
It is close to 50 years after the fall of fertility rate below replacement in Japan; so soon there will be increasing numbers of elders that not only do not have grandchildren, but don't have children either.
Coresidence of parents and children have fallen in half over two decades from 50% to 24%: https://academic.oup.com/psychsocgerontology/article/62/5/S3...
Here's the wikipedia article about elderly dying in Japan and being undiscovered due to being lonely and forgotten: https://en.wikipedia.org/wiki/Kodokushi