To save a few dollars and have the internet while out and about, we opted to buy sim cards for our mobile phones while in Japan. The sim cards have unlimited data and can be used for 15 days once activated. Costing AUD $30 per card.
This deal was found on Amazon Australia with the company Lemon Mobile.
Originally, we tried the company CUniq, but after having complications with payment (as they would only accept Visa and after trying two varieties of Visa gift cards, one from the supermarket and another from the Australian Post Office which required credentials, only to discover that neither worked), we looked elsewhere.
The deal on Amazon turned out to be better. We also received the cards within a couple of days.