It's called Christmas Eve by Tatsuro Yamashita. It's of course a very popular song there and has been for the past 23 1/2 years. They play this song at local JR stations and KFCs in Japan around Christmas time. He also did an English version.
Give the song a try, you'll really like it.
Here is the English version.
http://youtube.com/watch?v=0lAfDdKueM8
and here's the Japanese version
http://youtube.com/watch?v=RejXivHvgqY
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