Also in Japan it's Christmas Day, which is about as important an actual day as New Years day is in the U.S.
People usually do their celebrating on christmas eve, while christmas day is more or less morning stuff and then to work.
Hell the only reason most businesses actually give Christmas off to their employees in Japan is because it conveniently falls the day before the Emperor's birthday. In fact that being an actual national holiday is why they're doing it now and not the day after christmas...because THAT is a bigger holiday (for time off) for them!
Now, New Years on the other hand...don't expect ANYTHING to get done until January 5th if it involves a Japanese company.