If you have PR, make sure you get a Re-Entry Permit from the Immigration
(Some people didn't and got caught by Covid Travel Restrictions)
Re-Entry Permit will mean you will need to come back to Japan every 5 years or so to renew Re-Entry Permit and Zairyu Card
So long as you do that you can keep your PR forever.
You will have to consider tax implications, as you will have a liability to Japan taxes.
If you surrender your Zairyu Card, you would have to consider the Exit Tax.
If you have more than Y100M in assets, then you would have to mark to market and pay Capital Gains Tax on the paper gain...
But not if you keep your PR.
You will have to nominate a Tax Representative, and you will still be liable for Resident's Taxes for about 18 months after you leave.
They will send your Proxy payment slips to pay either in one shot, or quarterly.
i.e. you are currently paying Resident's Taxes on 2020 income, payable from July 2021 to June 2022.
If you are resident in a Ku-Shi-Cho-Son on Jan 1 2022, then you will be liable for Resident's Taxes on 2021 Income, payable from July 2022 to June 2023... If not, you won't...
Pension Payments you made into the Japanese Pension System; If you paid for just a few years, you could claim a refund when you left Japan, but you have paid more than you would get in refund, max 5 years, so not recommended.
https://www.nenkin.go.jp/international/ ... yment.html
https://www.nenkin.go.jp/international/ ... iles/A.pdf
You need to pay a minimum of 10 years (120 Months) contributions to qualify to get any Japanese Pension (120/480 x Japanese Pension Amount at Retirement age 67), so you probably want to get your contributions up to the minimum 120 months before age 60... The more the better. You can take the Pension anywhere in the world. You just have to process the application in Japan.
https://www.nenkin.go.jp/international/ ... nsion.html
You should Pay UK NI Cat 3 contributions for your time in Japan, and then continue to fund the UK Pension to retirement.
Alteratively, there is a Pension Agreement between Japan and UK, and you would have to work out how to get credit for Japan contributions... I don't recommend this... Get Both Pensions...
Others would have to comment on iDECO and NISA.
I don't think you will be able to contribute whilst not in Japan.