Thermae Romae has one of the best out there.
> I thought Japan censors everything, even classical art.
...are you dumb?
Just speaking from personal experience during my time in Japan. Everything I saw there (during class, in books, on tv, in museums) was censored, cropped or they chose to display another part of that scroll that didn't show anything explict. The uncesored stuff was usually locked away and you needed a special permission to access it.
Although I have to admit that I didn't pay any attention to western art while I was there. That's why I was so surprised by that cover.