Internet connections could be the first necessity during your stay in Tokyo. Here is some useful information on Free Wifi in Tokyo.
This is an app for both iOS/Android. After an easy registration, you can get a free WiFi access in Japan. It can be used in most of the Tokyo area or you can search a WiFi hot spot on the app. If you like to use the internet from landing at the airport, you need to install the app on your device before your arrival to Japan.
Visit this link for the detailed instruction and the links to the app for both iOS/Android.
Not all the stores but Starbucks coffee has a free WiFi service with a registration of your email address or Facebook account. The store with the logo above has the free WiFi service.