✔ 最佳答案
Since HK is using 200-220V but Japan is using 110-120V, so first of all you gotta make sure your appliances are compatible with both voltages (universal voltage). If not, even you have the right adapter, the appliances won't work!
If they've universal voltage then all you need is a plug adapter that can fit into the socket in Japan. (simply get one from any hardware/electronics store in HK) You just need one adapter, and as you said, a powerbar (拖板) would let you fit more appliances.
(Have fun in Japan!)