Christmas or クリスマス or "kurisumasu" in Japan closely resembles Christmas in the US, but works very differently (shouldn't be surprised). It comes with all of the sensory trappings of an American Christmas that I'm used to, but the Christian aspect really isn't seen anywhere, and Santa leaves gifts differently, and it's actually about going on dates, but people still buy each other presents, and the 25th goes virtually unobserved and...

So the Christian thing is a no brainer. Christians make up about 1% of the population in Japan which means 1) a little heart to heart with your hegemonic worldview might be in order, and 2) the "true meaning of Christmas" is lost on many people. You might think, "Oh, well I'm sure everyone at least knows it's the day Jesus was born and that's why we're celebrating it in the West." Definitely not everyone. The kids sure don't. As for how many aren't aware, I can't speak for the entire Japanese population, but I do know that last night (Christmas Eve) my host family celebrated with a Christmas cake complete with Santa effigy and candles, and that after a brief "what now" moment, we sang Happy Birthday to Santa.

I will say that the Christmas decorations are top notch. It might just be my proximity to Tokyo, but some of the Christmas lights I've seen rival what I see at home. That ties into what is probably the biggest theme of Christmas in Japan, the Christmas Eve date. Christmas in Japan is often referred to as a "lover's holiday," because anyone in a dating relationship will inevitably be out enjoying the night and decorations on Christmas Eve.

Notice Christmas Eve is the day to get excited over. Christmas day really has nothing to offer, because whatever you did on Christmas Eve (a date, Christmas party, home with the Christmas cake, or drinking) is now over. You're now in the limbo that is the week between Christmas and New Years.

What about presents? There's not typically a tree to pile gifts under or stockings to hang over the non-existent fireplace, though both of these things are still seen everywhere in the holiday imagery. Santa will lay a child's gift by the bed. Also, from what I understand, you don't have the Christmas morning family tradition of everyone opening gifts together. Christmas gifts among adults are handled just like any of the other hundreds of gift giving occasions in Japanese society.

So to sum up, I wouldn't say that there's any special Japanese "spin" on Christmas. It's just completely secular. I wouldn't expect Christmas in the US to be any different if you were to somehow suck the Christianity out of it. It would just make sense to go on dates and celebrate with elaborate cakes.