There are various options to have a cell phone in Japan, such as signing a new contract with a major cell phone carrier, buying a SIM card or renting a mobile Wi-Fi.
We have 3 major cell phone carriers in Japan. You can find instructions on how to sign up for a cell phone in the webpages below.
The following documents are required to sign up:
To purchase a general SIM card needs a contract procedure, and you usually pay the bill with a credit card or bank transfer. On the other hand, a prepaid SIM card can be easily purchased at convenience stores or airports, etc. though there is a limit to the amount of data.