Rather than the 28th, I'd suggest Japan (or more precisely Tokyo) goes quiet from the 30th onwards - until the 2nd/3rd January.

Christmas Eve is pretty cheesy and horrible as it has been turned into another Valentines day. This means the restaurants are doing special 'silly price' menus which you're expected to book for and pay through the nose for. When you wander around on the evening, you just see couples silently eating together and looking really miserable. The Xmas lights can be very pretty in Tokyo, but there's a tangible lack of festive cheer.

Otherwise, what I have noticed is an undercurrent of tension around this time. It's business as normal, but there is a tremendous pressure on everyone working to get everything in order so that the New Year can be started in the 'right' way. Office workers put in a lot of extra hours to meet these deadlines and people look tired and drained. Housewives will have spring cleaned their homes.

From the 30th/31st December the banks/postoffices start to close and it's almost impossible to get any money out ATMs. Families come to together (it's traditional to eat especially made longer noodles on the 31st) and then go out to visit their local shrine - either late that night or early next morning. There are parties going on in areas frequented by expats, such as Roppongi, and there must be some things going on in Shibuya as its the only time I've seen the area strewn with litter. However, I've spent the last few years visiting Meiji Jingu with my partner, and we take our visit pretty seriously.

A few shops in extremely central areas are open on the first, otherwise shops will only start to open on the 2nd or 3rd. You can buy bargain 'lucky bags' at this time, but availability is extremely limited. (You generally get mystery goods at a third or a quarter of the retail price).

I'm afraid I've no idea about Osaka - however, as more people 'go home' to Osaka to be with their families (as. opposed to Tokyo from which there is a year end exodus) I'd venture to guess that the atmosphere might be more, err.. 'festive?'