December 23 is a national holiday in Japan. The timing is completely unrelated to Christmas, something essentially uncelebrated here, but is a celebration of the Emperor's birthday. For some holidays throughout the year, had they fallen on a Sunday they would have, by law, been moved to Monday to ensure everyone has the day to relax. Not in this case though. This is known as the "Happy Monday" law which in it's own right is also unrelated to the 1980s English indie rock band.
December 23 also stands out for one other reason. In 1948, after a series of trials in Tokyo, the seven remaining key protagonists of the Pacific war were finally executed having been sentenced the previous November. The date was no coincidence. December 23 was chosen specifically because it was the then Emperor Hirohito's son's birthday. The allies knew that no one would celebrate martyrdom for these individuals on the Emperor's birthday in the years to come. And 65 years later they were right.