Paying taxes on foreign income in Japan

Hi, I have a question regarding the taxation of foreign income in Japan.
I will be on a student visa in japan (so I guess I qualify as a non-permanent resident?), and continue to work part-time for my company in Denmark (so it'll be remote work). They will continue to pay my salary to my danish bank account. When I called the danish tax office, they told me I don't have to pay any taxes to danish authorities as long as I can submit a document from the japanese authorities that I am paying taxes in japan instead.
Now, how do I get that document? Since my employer isn't japanese, the taxes won't be deducted automatically, and I think I will have to file a tax return form at some point. Can I register myself somewhere with the japanese government, to signalize that I will pay my taxes with the tax return when the time comes? Do I have to go to a specific office? And does anyone happen to know what it means when there is a tax agreement between Denmark and Japan? Some websites suggest i might not even have to pay any taxes at all as a non-permanent resident with foreign income.

Any advice on this topic is appreciated, as I can't really find information on the internet.