I'm sure the PH will have some nice decorations and there will be lots of illuminations and other decorations around the city. Japan is already moving into Christmas mode, with decorations starting to appear at amusement parks and some shopping centers. As Christmas is not a holiday, nowhere will there be any shorter operating hours. Christmas eve is a date night type of thing, and hotels and restaurants will be a bit fuller with younger types. I would expect the Twilight Time happy hour to be very crowded on 12/24.

Note however that in Japan Christmas season ends on 12/25, and except for the amusement parks much of the decorations, especially at places with fewer foreign clientele, will start to come down on 12/26 in preparation for the end of the year and New Years. Some facilities (minor museums, etc.) will start closing from around 12/28.