Pocket Wi-Fi is a mobile internet device that you can connect devices to via Wi-Fi while you are on the move in Japan. Pocket Wi-Fi, also known as Mi-Fi is routinely used in Japan but requires a cellular connection or SIM card holding device. Many accommodation hosts in Japan, will provide international guests with a pocket Wi-Fi device so they can use mobile internet, even though they don’t have a cellphone contract or device of their own.