WAmazing is a recently launched company in Japan offering free sim cards with 500MB of data to tourists. However, there are a few restrictions:
- iPhone 5/6/7 only
- Must download app and register at least two months prior to arrival
- Can only be collected from Narita (Tokyo) airport. (may expand later)
- Everything appears to be in Chinese language
If you can deal with all of those things though it's a pretty good deal considering the usual prices of data sims in Japan. It uses the Docomo network which has the best coverage out of all networks in Japan.