You initially pay this out of Post Tax Income, but you can claim the contributions as a Tax Deduction against Taxable Income, so that you actually pay this out of Pre-Tax income so would get any withheld income tax back as a refund at the end of the year, so the government pays the tax portion.
Depending on Tax Band.... 5.105%, 10.21%, 20.42%, 23.483%, 33.693%, 40.84%, or 45.945%... if the contributions fall within a single band...
However, you also get the deduction against your Residents' Taxes at 10%
Therefore, it only costs you roughly say
Y659,183 and the goverment pays the other Y331,816
or
Y558,002 and the goverment pays the other Y432,997
And, you can drop the refund into NISA tax free.
If you don't pay these voluntary contributions, you don't get any tax refund.
Your equivalent NISA investment will cost the Post Tax ¥991,000
This is for the Kiso Nenkin - Basic Pension
https://www.nenkin.go.jp/international/ ... nsion.html
But differs for the Kosei Nenkin - Employee's Pension
https://www.nenkin.go.jp/international/ ... loyee.html
See the sections
Benefits
Old-age Employees' Pension for age 60-64
and
Old-age Employees' Pension after age 65