I can't be very helpful as I was mainly there to explore underground tunnels and go places I shouldn't, but the cable car up the mountain is good in Hong Kong. Also drinks and food around Causeway Bay in the evening is quite nice, and they have a laser light show over the bay in the evening. A shame I only had a few days as I'd like to have stayed longer.
In Japan I had a few days in Tokyo around the Shinjuku area. Quite lively at night, pretty crazy area. Then I rented a car with a friend and drove north, stopped by the big Honda museum then went up to the area affected by the earthquake and tsunami 5 years ago. It's insane there, you can drive right through the red zone. From there we went north to find a derelict power station in the countryside and finally drove back to Tokyo for one night. We did want to go down to the suicide forest or whatever it's called, and also Mt Fuji, but again not enough time.