Use your UK electrical appliances in all Japanese plug sockets with the travel adapter from specialists Go Travel. Japan uses the USA style plugs which is two vertical flat pins with a semicircle top pin for earthing. However unique to Japan is that the majority of sockets in dwellings only allow unearthed plugs such as this one. If you try and use a USA style earthed adapter with 3 pins it will NOT fit in this socket. The majority of travel appliances do not need to be earthed so this isn't a problem.
You can check if you're appliance is ok for unearthed plugs by looking for the double earthed symbol on it which is a square within a square.