Taxes have to be paid somewhere, and if they don't pay taxes in Japan on your behalf (as korean and vietnam do on their respective countries I believe) that means that you have no tax credit whatsoever and you are then liable for full taxes in you own country
That is not necessarily true. Tax law varies widely from country to country. It all depends on where you are from, where you are living, and how often you go back to that country.
In my instance, I am a US citizen who is now living in another Asian country. My first $91,000 is tax free and I have so many deductions that my tax liability is very low in the US. My current home does not require any taxes to be paid unless I earn income here or am here for more than 180 days a year, which I am not. And I have no tax liability in Japan because I am only there as a crew member on a shore pass.
Taxes are complicated and I would recommend seeking professional advice from someone in your home country.