WH-Visa & earning royalties in home country

I'm currently on a working holiday visa in Japan. I'm a musician and receive royalties from the songs I've produced during the last decade which are paid to my bank account in my home country (EU citizen). My artistic activity is registered in my home country of course.
At the moment I'm still writing music but haven't published it, thus haven't made any money through songwriting I did in Japan. I also don't transfer my income to my Japanese bank account, only what is necessary to pay for national health insurance.
Do I need to report this type of income?

by Super-Artichoke6761