score:5
but is one not supposed to not return to Japan, for a period of time, after departing for the first time?
No, there is no such rule. If staying for 90 days and returning after a daytrip, they would be suspicious, of course, as it would look like you're living in Japan through visa runs, but not during such a short visit.
You will be good.
Upvote:2
By holding an Polish/EU passport, you do not need a visa to enter Japan for short term visits - 90 days. The same applies to visiting South Korea. So you should be fine.