Sunday is a completely regular work/school day. Weekend is (sortof) Friday and then Saturday. School on Friday generally only runs until noon, even for the higher grades. Colleges are closed on Friday.
I haven’t seen any Government Offices open on Friday for the longest time; bank branches are generally open 5 days a week, but some (mostly those who cater to clients whose business is to a large extent overseas) are closed Sunday (the only exception I know to the “Sunday is a workday” rule) instead of Friday.
Japanese stores are typically closed once a week, with the day varying from store to store. For example, my local bakery in Wakayama was closed every Wednesday and every other Thursday, while all the stores in the local shopping arcade were closed on Mondays. It’s not an unusual occurance to head off eager to visit a shop you rarely frequent to discover it’s closed.
I believe offices and the like nominally have a 5 day work week, but would not be surprised if many “voluntarily” work more days.
Just a footnote.
Ancient Rome had no regular day of rest but quite a few holidays.
They didn’t need a day of rest? Slaves did all the work!