Yeah government site is offline and says shall be back in October but I'm not sure whether it's last October maybe

According the link you provided it seems most brokers take 171 yen/month and 2052 yen/year.
The next question then - do they take this amount even if you have left Japan which means you can not add any money and can only "re-balance"? They still gonna take those couple thousands, every year?

Regarding pension, if it's 10 years, yeah maybe I should consider. Especially since 3 years are paid, already...
I was simply told it's minimum 20 years, before. Shall do some research. Thanks!!