I travel to Japan on occasion and was there this past December and then again in February. I watched the Diamond Princess-Covid plague ship story unfold while I was there.
I actually don't have much to add as my trips to Japan are always for business, but my experience is that Japan is truly a whole different world. I also travel to Europe quite a bit and that is "foreign" but you don't feel so out of place (i.e. they will think you are a local until you open your mouth). That doesn't happen in Japan.
My business is always in Tokai-mura (Ibaraki prefecture). About two hours north of Tokyo by bus. Public transport is very good, but it can be hard to figure out exactly what is going on, sometimes. I've stood nervously on many train platforms hoping I'm on the right one. You'll need cash. In fact, I would assume you need to pay in cash and I typically ask if a card is OK prior to making a purchase.
The Japanese are very polite and respectful. It is a strong part of their culture. One bit of advice is to brush up on these customs and be very respectful also. For instance, it is disrespectful to talk loudly (or really at all) on public transport. I've been on packed trains where it was silent other than the sounds of the train itself.