Japanese families are largely not multigenerational in the same house.

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