
This tradition appears to have started in the mid-seventies, when they started promoting Christmas meals apparently after some foreigners ended up at KFC on Christmas day when they couldn't find turkey in Japan (it is still hard to find turkey, but in recent years we are seeing it in a few more stores).
Christmas is not an actual holiday in Japan. Most people work on the 25th and in recent years the Japanese school year starts their winter break after Christmas. In Japan, New Years is the big family holiday. Everyone comes home for New Years. Christmas was often thought of as a romantic date night. It is still popular for couples today.
Young families began celebrating Christmas in the Western way (North American and UK). The image of Christmas is chicken and Christmas cake. (Subject of a whole other blog). An added bonus is that starting in December, the statues of the Colonel outside most KFC restaurants are dressed up like Santa.
KFC is now the standard for Christmas meals, offering a decorated bucket of chicken with salad, Christmas cake, biscuits, and a collectors plate. These buckets are so popular, you can begin making reservations early in December.
Since we moved to the town we are living in now and have a KFC less than a 5 minute bike ride away, we have started doing this tradition again. Our family likes KFC, but most of the year the meals are just chicken and fries (and a little pricy for fast food). So we reserved a bucket, and on Christmas day, at the appointed time, someone will bike over and pick it up.