Looking for some advice in planning and investing as a US citizen planning to move to Japan

Hello!

I’ve been doing my own research, but I’m a complete beginner to investing/taxes, so it’s all a bit overwhelming.

I am currently a US citizen with plans to move to Japan in the future. I would like to say I want to retire in Japan, but that’s a very long time away so I’m honestly uncertain about where the end goal is.

I am aware that a Roth IRA may not be a favorable investment if one plans to retire in Japan, but how bad is it really? I know that there are still some uncertainties about how it is taxed in Japan, but if the Roth IRA is taxed on withdrawal, is it not effectively the same as a taxable brokerage account?

My current investments are a 401(k), Roth IRA, and a regular brokerage where I plan to invest in ETFs.

Are these solid investments I can make right now as an American if I want to retire in Japan, or are there any others I can consider? Since I’m still unsure of where I want to retire, I’d like to set myself up for success in either country as much as possible with my investments.

Any advice and insight would be greatly appreciated, thank you!