Here is Japan's population "pyramid."
You will note it is not pyramid shaped and this is a problem.
People start receiving their national pension payments at age 65 aka about 30% of Japan.
Add to that children 0-15 who definitely aren't paying into the pension system, that makes over 40% of the country drawing from state coffers.
That means nearly every Japanese worker - that includes teenagers btw - not only have to support themselves on their income, but another Japanese person as well.
Indeed Japan has the worst dependency ratio in the world, with Finland and Italy tied for second:
https://en.wikipedia.org/wiki/List_of_countries_by_dependency_ratio
If workers are all paying higher taxes to keep the elderly alive, they don't have money to raise children so the problem only gets worse until said elderly do everyone a favor and die already.
The sooner that happens, the better. Ergo encouraging boomers to kill themselves is everyone's patriotic duty.