We have a group of friends(including Japanese). We organize a party in which each family bring some home made dishes. We will make our own cake there and enjoy some hours together. Children will exchange gifts between them and also the Santa Claus will give some small gifts to each of them. Its a wonderful celebration that is conducted every year, usually on X'mas night.
Working! It is one of the things I love about Japan. December 24 and 25, if they fall on a weekday, are regular working days. I love the "normality" of the day. If Christmas can be just like any other day, then maybe it is easier to "make everyday Christmas" as they say. So yes, we work and the kids go to school, and then we have a nicer than usual dinner for Christmas Eve, and bring out the Christmas plates and placemats for a more festive meal. Weird as it is, we also have a Christmas Cake (a Japanese tradition probably started by a cake chain), but cake anytime is always nice. On Christmas morning, the kids get "surprised" by the presents left by Santa and they get to open them before they go to school.