As Japan is not a Christian country, Christmas isn't a national holiday there, and the religious part of the festival is not celebrated except by the country's small Christian minority (who often spend the day doing charity work rather than celebrating at home). However, as a secular festival and fun day, Christmas has been very popular in Japan for many years now.
Christmas Eve is popular with young couples, who often go out for a romantic meal together. For the day itself, there are some typical Christmas traditions with a Japanese style: For example, there is a Buddhist Santa (there is a separate Beuddhist tradition of a gift-giving figure, similar to Santa, but Japanese people also enjoy the 'western' Santa tradition), and a special Christmas cake with tree and flower decorations. Favourite Christmas meals include fried chicken, and Christmas lights and decorations can be seen in shops and public places.
However, Christmas is less important in Japan than New Year.