The voltage used throughout Japan is uniformly 100 volts, A.C. There are two kinds of frequencies in use; 50 Hertz in eastern Japan (including Tokyo) and 60 Hertz in western Japan (including Nagoya, Kyoto and Osaka). There are no columnar-shaped plugs or 3-pin plugs used in Japan but instead, exclusively 2-flat-pin plugs are used. It is therefore advised to purchase a plug adapter beforehand.
Reference：shapes of plugs used in the world; Type A for Japan
Wi-Fi System and Telecommunications for tourist
In Japan, it is comparatively hard to find a free Wi-Fi in most of the cities, not to mention small towns.
So, it is recommended to rent a portable Wi-Fi router for your stay in Japan. That will make an internet access easy and simple throughout Japan.
For more information regarding rental portable Wi-Fi router, please refer to the link below.
(It will cost approximately 11,000 – 16,000 yen for 30 days.)
You will even be allowed to drop it at the airport when you leave Japan. Please ask for more detailed information at a store.
For phones, a rechargeable telephone card will be highly recommended. A brand called Brastel is popular among foreign tourists (including students from UAEU). It will be very easy, as you will be given a Japanese phone number on your own smartphone by installing the Brastel card application. With that number, you will be able to make both domestic and international calls, and to recharge it online. For more information regarding Brastel card, please refer to the link below.