Christmas was first introduced in Japan by Christian missionaries in the late 1870s and was celebrated only by those who had accepted the Christian faith. Today, almost everyone in Japan accepts and celebrate Christmas, but the 25th of December is still a normal day in Japan.
Families decorate Christmas trees with fake snow (yes, it is winter in Japan and wishing for a white Christmas is a realistic one up there) and buy Christmas cake. They may have a special Christmas feast on Christmas Eve, mainly chicken instead of turkey, and some other traditional food.
Here are some images of Christmas in Japan. Watch out for different types of Christmas trees and cakes.