This question already has an answer here:
I will be visiting Japan for two weeks as a tourist. I would like to have Internet access on my phone at all times, and found that there are some mobile data options for tourists. How do they actually work? Especifically:
Can I bring my european phone, put the sim card in and it works or will I need to rent/buy a japanese terminal? How is the signal through Japan? Will it work only in big cities, on most populated areas or all through Japan? Where can I buy them? What is the cost and the data cap like? What is the process of geting one? Will I need to sign a contract, show them my ID and all that or can i just pay and get the card inmediatly?
This is all both to be able to make a decision beforehand if it is indeed worthwile and to make sure I dont get scammed once I get there.