At the end of November merchandising heralds the onset (onslaught?) of the season. Santa's show up in some advertising and Christmas carols can be heard in stores. (In English!) Also advertisements appear for special Christmas eve and Christmas day hotel & restaurant dinners and shows, generally with a strong romance theme. More and more Christmas lights are going up each year (probably a thousand per cent increase in the seven years we've been here) on stores and at malls, though I've seen few if any on private homes.
Christmas trees (artificial --- there is no live Christmas tree market) however, have begun to appear in the occasional home, and can be bought in big department stores. Santa does not yet appear in person, only as an advertising foil. And the airwaves are not clogged with TV specials.
There are two special Japanese Christmas customs:
First, the Daiku, or Great Nine, which refers to Beethoven's Ninth Symphony. This is traditionally performed in many places at Christmas time (though probably as much in conjuction with the New Year), sometimes with huge massed choruses for the famous part with what American Christians sing as a hymn --- Joyful, Joyful, We Adore Thee.
The second custom is the Christmas Cake. Yes, friends, what Christmas would be complete without its Christmas Cake? How have you survived without one so long? Well, it's a blessing to the Japanese bakery industry, that's for sure, because this is not a home project. One buys it. And the Japanese are generally slack jawed when told that America knows no Christmas Cake and it's a Japanese custom.
Christmas is basically overshadowed by New Year's celebrations, sort of the opposite of America. In Japan Christmas is a subsidiary holiday, most treasured by merchants, I think. Christmas day, for example is not a holiday from work. Hence, most churches will have their special Christmas worship services on the nearest Sunday before the 25th and perhaps on Christmas eve.
Most Japanese naturally have a weak understanding of Christmas's religious roots and customs. I remember one Japanese pastor being asked if it's Santa's birthday. Christianity is respected in Japan but hardly known at all, which is not too surprising with less than 1% being Christian. However, many Japanese are interested in American Christmas customs and some Japanese churches take advantage of this to meet new Japanese and introduce them to Christmas, Jesus, and their church. For example, I work with a small (averaging 30 people on a Sunday morning) church in Misato, that has a special Candle Service, two kids meetings, three American Christmas programs, lots of special Christmas decorations and a gift pack handout for all guests during December. Through this they draw an extra 300-400 people to church.