Foreign income while going to language school

I am planning on doing a sabbatical and going to Japan to study for a year. My employer has this model where you can kind of "store" your salary for a time and then get it paid later. E.g. you work for 6 months, get only 50% of your salary, but then get the other 50% for the next 6 months. (I live in Germany)

If I did this and got income from my german company during the sabbatical, would I have to file taxes in japan, even though technically I am not working there? Has anyone done anything similar to this?

by OwOsaurus